diff --git a/src/Mod/Sketcher/Gui/CommandConstraints.cpp b/src/Mod/Sketcher/Gui/CommandConstraints.cpp
index a12cdbfb14..9d36ddc088 100644
--- a/src/Mod/Sketcher/Gui/CommandConstraints.cpp
+++ b/src/Mod/Sketcher/Gui/CommandConstraints.cpp
@@ -228,6 +228,12 @@ void showNoConstraintBetweenExternal()
                          QObject::tr("Cannot add a constraint between two external geometries!"));    
 }
 
+void showNoConstraintBetweenFixedGeometry()
+{
+    QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Wrong selection"),
+                         QObject::tr("Cannot add a constraint between two fixed geometries! Fixed geometries involve external geometry, blocked geometry or special points as B-Spline knot points."));    
+}
+
 bool SketcherGui::checkBothExternal(int GeoId1, int GeoId2)
 {
     if (GeoId1 == Constraint::GeoUndef || GeoId2 == Constraint::GeoUndef)
@@ -245,6 +251,39 @@ bool SketcherGui::checkBothExternalOrConstructionPoints(const Sketcher::SketchOb
         (GeoId1 < 0 && isConstructionPoint(Obj,GeoId2)) || (GeoId2 < 0 && isConstructionPoint(Obj,GeoId1));
 }
 
+bool SketcherGui::isPointOrSegmentFixed(const Sketcher::SketchObject* Obj, int GeoId) 
+{ 
+    const std::vector< Sketcher::Constraint * > &vals = Obj->Constraints.getValues();
+    
+    if (GeoId == Constraint::GeoUndef)
+        return false;
+    else    
+	return checkConstraint(vals, Sketcher::Blocked, GeoId, Sketcher::none) || GeoId <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId);
+}
+
+bool SketcherGui::areBothPointsOrSegmentsFixed(const Sketcher::SketchObject* Obj, int GeoId1, int GeoId2) 
+{ 
+    const std::vector< Sketcher::Constraint * > &vals = Obj->Constraints.getValues();
+    
+    if (GeoId1 == Constraint::GeoUndef || GeoId2 == Constraint::GeoUndef)
+        return false;
+    else    
+	return (  (checkConstraint(vals, Sketcher::Blocked, GeoId1, Sketcher::none) || GeoId1 <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId1)) &&
+		  (checkConstraint(vals, Sketcher::Blocked, GeoId2, Sketcher::none) || GeoId2 <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId2)));
+}
+
+bool SketcherGui::areAllPointsOrSegmentsFixed(const Sketcher::SketchObject* Obj, int GeoId1, int GeoId2, int GeoId3)
+{
+    const std::vector< Sketcher::Constraint * > &vals = Obj->Constraints.getValues();
+    
+    if (GeoId1 == Constraint::GeoUndef || GeoId2 == Constraint::GeoUndef || GeoId3 == Constraint::GeoUndef)
+        return false;
+    else    
+	return (  (checkConstraint(vals, Sketcher::Blocked, GeoId1, Sketcher::none) || GeoId1 <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId1)) &&
+		  (checkConstraint(vals, Sketcher::Blocked, GeoId2, Sketcher::none) || GeoId2 <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId2)) &&	
+		  (checkConstraint(vals, Sketcher::Blocked, GeoId3, Sketcher::none) || GeoId3 <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId3)));  
+}
+
 void SketcherGui::getIdsFromName(const std::string &name, const Sketcher::SketchObject* Obj,
                     int &GeoId, PointPos &PosId)
 {
@@ -642,6 +681,17 @@ void SketcherGui::tryAutoRecomputeIfNotSolve(Sketcher::SketchObject* obj)
         obj->solve();
 }
 
+bool SketcherGui::checkConstraint(const std::vector< Sketcher::Constraint * > &vals, ConstraintType type, int geoid, PointPos pos) 
+{
+    for (std::vector< Sketcher::Constraint * >::const_iterator itc= vals.begin(); itc != vals.end(); ++itc) {
+	if ((*itc)->Type == type && (*itc)->First == geoid && (*itc)->FirstPos == pos){
+	    return true;
+	}
+    }
+  
+    return false;
+}
+
 
 namespace SketcherGui {
 
@@ -1155,7 +1205,7 @@ void CmdSketcherConstrainHorizontal::activated(int iMsg)
                 return;
             }
 
-            // check if the edge has already a Horizontal or Vertical constraint
+            // check if the edge has already a Horizontal/Vertical/Block constraint
             for (std::vector< Sketcher::Constraint * >::const_iterator it= vals.begin();
                  it != vals.end(); ++it) {
                 if ((*it)->Type == Sketcher::Horizontal && (*it)->First == GeoId && (*it)->FirstPos == Sketcher::none){
@@ -1168,13 +1218,19 @@ void CmdSketcherConstrainHorizontal::activated(int iMsg)
                                          QObject::tr("The selected edge has already a vertical constraint!"));
                     return;
                 }
+		// check if the edge has already a Blocked constraint
+		if ((*it)->Type == Sketcher::Blocked && (*it)->First == GeoId && (*it)->FirstPos == Sketcher::none) {
+		  QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Impossible constraint"),
+					QObject::tr("The selected edge has already a Block constraint!"));
+		  return;
+		}
             }
             edgegeoids.push_back(GeoId);
         }
         else if(isVertex(GeoId,PosId)) {
             // can be a point, a construction point, an external point or root
 
-            if(GeoId < 0 || isConstructionPoint(Obj,GeoId))
+            if(isPointOrSegmentFixed(Obj, GeoId))
                 fixedpoints++;
 
             pointgeoids.push_back(GeoId);
@@ -1209,6 +1265,11 @@ void CmdSketcherConstrainHorizontal::activated(int iMsg)
             ,selection[0].getFeatName(),*it,*itp,*std::next(it),*std::next(itp));
         }
     }
+    else { // vertex mode, fixedpoints > 1
+	QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Impossible constraint"),
+			    QObject::tr("There are more than one fixed point selected. Select a maximum of one fixed point!"));
+	return;      
+    }
     // finish the transaction and update
     commitCommand();
 
@@ -1237,7 +1298,7 @@ void CmdSketcherConstrainHorizontal::applyConstraint(std::vector<SelIdPair> &sel
                 return;
             }
 
-            // check if the edge has already a Horizontal or Vertical constraint
+            // check if the edge has already a Horizontal/Vertical/Blocked constraint
             for (std::vector< Sketcher::Constraint * >::const_iterator it= vals.begin();
                  it != vals.end(); ++it) {
                 if ((*it)->Type == Sketcher::Horizontal && (*it)->First == CrvId){
@@ -1250,6 +1311,12 @@ void CmdSketcherConstrainHorizontal::applyConstraint(std::vector<SelIdPair> &sel
                                          QObject::tr("The selected edge has already a vertical constraint!"));
                     return;
                 }
+		// check if the edge has already a Blocked constraint
+		if ((*it)->Type == Sketcher::Blocked && (*it)->First == CrvId && (*it)->FirstPos == Sketcher::none) {
+		  QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Impossible constraint"),
+					QObject::tr("The selected edge has already a Block constraint!"));
+		  return;
+		}    
             }
 
             // undo command open
@@ -1385,7 +1452,7 @@ void CmdSketcherConstrainVertical::activated(int iMsg)
                 return;
             }
             
-            // check if the edge has already a Horizontal or Vertical constraint
+            // check if the edge has already a Horizontal/Vertical/Block constraint
             for (std::vector< Sketcher::Constraint * >::const_iterator it= vals.begin();
                  it != vals.end(); ++it) {
                 if ((*it)->Type == Sketcher::Vertical && (*it)->First == GeoId && (*it)->FirstPos == Sketcher::none){
@@ -1398,13 +1465,19 @@ void CmdSketcherConstrainVertical::activated(int iMsg)
                                          QObject::tr("The selected edge has already a horizontral constraint!"));
                     return;
                 }
-                 }
-                 edgegeoids.push_back(GeoId);
+		// check if the edge has already a Blocked constraint
+		if ((*it)->Type == Sketcher::Blocked && (*it)->First == GeoId && (*it)->FirstPos == Sketcher::none) {
+		  QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Impossible constraint"),
+					QObject::tr("The selected edge has already a Block constraint!"));
+		  return;
+		}         
+            }
+            edgegeoids.push_back(GeoId);
         }
         else if(isVertex(GeoId,PosId)) {
-            // can be a point, a construction point, an external point or root
-            
-            if(GeoId < 0 || isConstructionPoint(Obj,GeoId))
+            // can be a point, a construction point, an external point, root or a blocked geometry
+              
+            if(isPointOrSegmentFixed(Obj, GeoId))
                 fixedpoints++;
             
             pointgeoids.push_back(GeoId);
@@ -1428,7 +1501,7 @@ void CmdSketcherConstrainVertical::activated(int iMsg)
             ,selection[0].getFeatName(),*it);
         }
     }
-    else if (fixedpoints <= 1) { // pointgeoids
+    else if (fixedpoints <= 1) { // vertex mode, maximum one fixed point
         // undo command open
         openCommand("add vertical alignment");
         std::vector<int>::iterator it;
@@ -1439,6 +1512,11 @@ void CmdSketcherConstrainVertical::activated(int iMsg)
             ,selection[0].getFeatName(),*it,*itp,*std::next(it),*std::next(itp));
         }
     }
+    else { // vertex mode, fixedpoints > 1
+	QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Impossible constraint"),
+			    QObject::tr("There are more than one fixed point selected. Select a maximum of one fixed point!"));
+	return;      
+    }
     // finish the transaction and update
     commitCommand();
 
@@ -1480,6 +1558,12 @@ void CmdSketcherConstrainVertical::applyConstraint(std::vector<SelIdPair> &selSe
                                          QObject::tr("The selected edge has already a vertical constraint!"));
                     return;
                 }
+		// check if the edge has already a Blocked constraint
+		if ((*it)->Type == Sketcher::Blocked && (*it)->First == CrvId && (*it)->FirstPos == Sketcher::none) {
+		  QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Impossible constraint"),
+					QObject::tr("The selected edge has already a Block constraint!"));
+		  return;
+		}                
             }
 
             // undo command open
@@ -1622,6 +1706,13 @@ void CmdSketcherConstrainLock::activated(int iMsg)
     int lastconstraintindex = Obj->Constraints.getSize()-1;
 
     if( GeoId.size() == 1 ) { // absolute mode
+      
+	// check if the edge has already a Blocked constraint
+	bool edgeisblocked = false;
+	
+	if ( isPointOrSegmentFixed(Obj, GeoId[0])) {
+	  edgeisblocked = true;
+	}
 
         Base::Vector3d pnt = Obj->getPoint(GeoId[0],PosId[0]);
 
@@ -1636,7 +1727,7 @@ void CmdSketcherConstrainLock::activated(int iMsg)
 
         lastconstraintindex+=2;
 
-        if (GeoId[0] <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId[0]) || constraintCreationMode==Reference) {
+        if (edgeisblocked || GeoId[0] <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId[0]) || constraintCreationMode==Reference) {
             // it is a constraint on a external line, make it non-driving
 
             Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -1651,9 +1742,20 @@ void CmdSketcherConstrainLock::activated(int iMsg)
         std::vector<Sketcher::PointPos>::const_iterator itp;
 
         Base::Vector3d pntr = Obj->getPoint(GeoId.back(),PosId.back());
+	
+	// check if the edge has already a Blocked constraint
+	bool refpointfixed = false;
+	    
+	if ( isPointOrSegmentFixed(Obj, GeoId.back()))
+	      refpointfixed = true;
 
         for (itg = GeoId.begin(), itp = PosId.begin(); itg != std::prev(GeoId.end()) && itp != std::prev(PosId.end()); ++itp, ++itg) {
 
+	    bool pointfixed = false;
+	    
+	    if ( isPointOrSegmentFixed(Obj, *itg))
+	      pointfixed = true;
+	    
             Base::Vector3d pnt = Obj->getPoint(*itg,*itp);
 
             // undo command open
@@ -1667,7 +1769,7 @@ void CmdSketcherConstrainLock::activated(int iMsg)
                                     selection[0].getFeatName(),*itg,*itp,GeoId.back(),PosId.back(),pntr.y-pnt.y);
             lastconstraintindex+=2;
 
-            if (*itg <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,*itg) || constraintCreationMode==Reference) {
+            if ( (refpointfixed && pointfixed) || constraintCreationMode==Reference) {
                 // it is a constraint on a external line, make it non-driving
 
                 Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -1694,6 +1796,12 @@ void CmdSketcherConstrainLock::applyConstraint(std::vector<SelIdPair> &selSeq, i
         // Create the constraints
         SketcherGui::ViewProviderSketch* sketchgui = static_cast<SketcherGui::ViewProviderSketch*>(getActiveGuiDocument()->getInEdit());
         Sketcher::SketchObject* Obj = sketchgui->getSketchObject();
+	
+	// check if the edge has already a Blocked constraint
+	bool pointfixed = false;
+	    
+	if ( isPointOrSegmentFixed(Obj, selSeq.front().GeoId))
+	    pointfixed = true;
 
         Base::Vector3d pnt = Obj->getPoint(selSeq.front().GeoId, selSeq.front().PosId);
 
@@ -1706,7 +1814,7 @@ void CmdSketcherConstrainLock::applyConstraint(std::vector<SelIdPair> &selSeq, i
             Gui::Command::Doc, "App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('DistanceY', %d, %d, %f)) ",
             sketchgui->getObject()->getNameInDocument(), selSeq.front().GeoId, selSeq.front().PosId, pnt.y);
 
-        if (selSeq.front().GeoId <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,selSeq.front().GeoId) || constraintCreationMode==Reference) {
+        if (pointfixed || constraintCreationMode==Reference) {
             // it is a constraint on a external line, make it non-driving
             const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
 
@@ -1847,12 +1955,12 @@ void CmdSketcherConstrainBlocked::activated(int iMsg)
     }
 
     std::vector<int> GeoId;
+    const std::vector< Sketcher::Constraint * > &vals = Obj->Constraints.getValues();
 
     for (std::vector<std::string>::const_iterator it = SubNames.begin(); it != SubNames.end(); ++it) {
         int GeoIdt;
         Sketcher::PointPos PosIdt;
         getIdsFromName((*it), Obj, GeoIdt, PosIdt);
-        GeoId.push_back(GeoIdt);
 
         if ( isVertex(GeoIdt,PosIdt) || GeoIdt < 0 ) {
             if(selection.size() == 1) {
@@ -1866,7 +1974,16 @@ void CmdSketcherConstrainBlocked::activated(int iMsg)
             // clear the selection
             getSelection().clearSelection();
             return;
-            }
+	}
+	
+	// check if the edge has already a Blocked constraint
+	if ( checkConstraint(vals, Sketcher::Blocked, GeoIdt, Sketcher::none)) {
+	  QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Double constraint"),
+	      QObject::tr("The selected edge has already a Block constraint!"));
+	  return;
+	}
+	
+	GeoId.push_back(GeoIdt);
     }
 
     for (std::vector<int>::iterator itg = GeoId.begin(); itg != GeoId.end(); ++itg) {
@@ -1906,6 +2023,15 @@ void CmdSketcherConstrainBlocked::applyConstraint(std::vector<SelIdPair> &selSeq
             // Create the constraints
             SketcherGui::ViewProviderSketch* sketchgui = static_cast<SketcherGui::ViewProviderSketch*>(getActiveGuiDocument()->getInEdit());
 
+	    // check if the edge has already a Blocked constraint
+	    const std::vector< Sketcher::Constraint * > &vals = static_cast<Sketcher::SketchObject *>(sketchgui->getObject())->Constraints.getValues();
+
+	    if ( checkConstraint(vals, Sketcher::Blocked, selSeq.front().GeoId, Sketcher::none)) {
+	      QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Double constraint"),
+		  QObject::tr("The selected edge has already a Block constraint!"));
+	      return;
+	    }
+    
             // undo command open
             openCommand("add blocked constraint");
 
@@ -2149,13 +2275,19 @@ void CmdSketcherConstrainCoincident::activated(int iMsg)
     int GeoId1, GeoId2;
     Sketcher::PointPos PosId1, PosId2;
     getIdsFromName(SubNames[0], Obj, GeoId1, PosId1);
-
+   
     // undo command open
     bool constraintsAdded = false;
     openCommand("add coincident constraint");
     for (std::size_t i=1; i<SubNames.size(); i++) {
         getIdsFromName(SubNames[i], Obj, GeoId2, PosId2);
 
+        // check if the edge has already a Blocked constraint
+	if ( areBothPointsOrSegmentsFixed(Obj,GeoId1,GeoId2) ) {
+	  showNoConstraintBetweenFixedGeometry();    
+	  return;
+	}
+    
         // check if this coincidence is already enforced (even indirectly)
         bool constraintExists=Obj->arePointsCoincident(GeoId1,PosId1,GeoId2,PosId2);
 
@@ -2190,6 +2322,12 @@ void CmdSketcherConstrainCoincident::applyConstraint(std::vector<SelIdPair> &sel
 
         int GeoId1 = selSeq.at(0).GeoId, GeoId2 = selSeq.at(1).GeoId;
         Sketcher::PointPos PosId1 = selSeq.at(0).PosId, PosId2 = selSeq.at(1).PosId;
+	
+	// check if the edge has already a Blocked constraint
+	if ( areBothPointsOrSegmentsFixed(Obj, GeoId1, GeoId2) ) {
+	  showNoConstraintBetweenFixedGeometry();
+	  return;
+	}
 
         // undo command open
         Gui::Command::openCommand("add coincident constraint");
@@ -2257,9 +2395,10 @@ void CmdSketcherConstrainDistance::activated(int iMsg)
         bool constraintMode = hGrp->GetBool("ContinuousConstraintMode", true);
 
         if (constraintMode) {
-        ActivateHandler(getActiveGuiDocument(),
-                new DrawSketchHandlerGenConstraint(constraintCursor, this));
-        getSelection().clearSelection();
+	    ActivateHandler(getActiveGuiDocument(),
+		    new DrawSketchHandlerGenConstraint(constraintCursor, this));
+	    
+	    getSelection().clearSelection();
         } else {
             QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Wrong selection"),
                                  QObject::tr("Select vertexes from the sketch."));
@@ -2283,7 +2422,7 @@ void CmdSketcherConstrainDistance::activated(int iMsg)
     if (SubNames.size() == 2)
         getIdsFromName(SubNames[1], Obj, GeoId2, PosId2);
     
-    bool bothexternalorconstructionpoints=checkBothExternalOrConstructionPoints(Obj,GeoId1, GeoId2);
+    bool arebothpointsorsegmentsfixed=areBothPointsOrSegmentsFixed(Obj,GeoId1, GeoId2);
     
     if (isVertex(GeoId1,PosId1) && (GeoId2 == Sketcher::GeoEnum::VAxis || GeoId2 == Sketcher::GeoEnum::HAxis)) {
         std::swap(GeoId1,GeoId2);
@@ -2297,6 +2436,7 @@ void CmdSketcherConstrainDistance::activated(int iMsg)
 
         if (GeoId1 == Sketcher::GeoEnum::HAxis && PosId1 == Sketcher::none) {
             PosId1 = Sketcher::start;
+	    
             openCommand("add distance from horizontal axis constraint");
             Gui::Command::doCommand(
                 Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('DistanceY',%d,%d,%d,%d,%f)) ",
@@ -2304,6 +2444,7 @@ void CmdSketcherConstrainDistance::activated(int iMsg)
         }
         else if (GeoId1 == Sketcher::GeoEnum::VAxis && PosId1 == Sketcher::none) {
             PosId1 = Sketcher::start;
+	    
             openCommand("add distance from vertical axis constraint");
             Gui::Command::doCommand(
                 Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('DistanceX',%d,%d,%d,%d,%f)) ",
@@ -2311,14 +2452,14 @@ void CmdSketcherConstrainDistance::activated(int iMsg)
         }
         else {
             Base::Vector3d pnt1 = Obj->getPoint(GeoId1,PosId1);
-
+	    
             openCommand("add point to point distance constraint");
             Gui::Command::doCommand(
                 Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('Distance',%d,%d,%d,%d,%f)) ",
                 selection[0].getFeatName(),GeoId1,PosId1,GeoId2,PosId2,(pnt2-pnt1).Length());
         }
         
-        if (bothexternalorconstructionpoints || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
+        if (arebothpointsorsegmentsfixed || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
             const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
             
             Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -2350,7 +2491,7 @@ void CmdSketcherConstrainDistance::activated(int iMsg)
                 Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('Distance',%d,%d,%d,%f)) ",
                 selection[0].getFeatName(),GeoId1,PosId1,GeoId2,ActDist);
 
-            if (bothexternalorconstructionpoints || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
+            if (arebothpointsorsegmentsfixed || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
                 const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
                 
                 Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -2369,19 +2510,21 @@ void CmdSketcherConstrainDistance::activated(int iMsg)
                                  QObject::tr("Cannot add a length constraint on an axis!"));
             return;
         }
+        
+        arebothpointsorsegmentsfixed=isPointOrSegmentFixed(Obj,GeoId1);
 
         const Part::Geometry *geom = Obj->getGeometry(GeoId1);
         if (geom->getTypeId() == Part::GeomLineSegment::getClassTypeId()) {
             const Part::GeomLineSegment *lineSeg;
             lineSeg = static_cast<const Part::GeomLineSegment*>(geom);
-            double ActLength = (lineSeg->getEndPoint()-lineSeg->getStartPoint()).Length();
+            double ActLength = (lineSeg->getEndPoint()-lineSeg->getStartPoint()).Length(); 
 
             openCommand("add length constraint");
             Gui::Command::doCommand(
                 Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('Distance',%d,%f)) ",
                 selection[0].getFeatName(),GeoId1,ActLength);
             
-            if (GeoId1 <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId1)|| constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
+            if (arebothpointsorsegmentsfixed || GeoId1 <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId1) || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
                 const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
                 
                 Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -2407,6 +2550,8 @@ void CmdSketcherConstrainDistance::applyConstraint(std::vector<SelIdPair> &selSe
 
     int GeoId1 = Constraint::GeoUndef, GeoId2 = Constraint::GeoUndef;
     Sketcher::PointPos PosId1 = Sketcher::none, PosId2 = Sketcher::none;
+    
+    bool arebothpointsorsegmentsfixed=areBothPointsOrSegmentsFixed(Obj,GeoId1, GeoId2);
 
     switch (seqIndex) {
     case 0: // {SelVertex, SelVertexOrRoot}
@@ -2419,6 +2564,7 @@ void CmdSketcherConstrainDistance::applyConstraint(std::vector<SelIdPair> &selSe
 
         if (GeoId1 == Sketcher::GeoEnum::HAxis && PosId1 == Sketcher::none) {
             PosId1 = Sketcher::start;
+	    
             openCommand("add distance from horizontal axis constraint");
             Gui::Command::doCommand(
                 Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('DistanceY',%d,%d,%d,%d,%f)) ",
@@ -2426,6 +2572,7 @@ void CmdSketcherConstrainDistance::applyConstraint(std::vector<SelIdPair> &selSe
         }
         else if (GeoId1 == Sketcher::GeoEnum::VAxis && PosId1 == Sketcher::none) {
             PosId1 = Sketcher::start;
+	    
             openCommand("add distance from vertical axis constraint");
             Gui::Command::doCommand(
                 Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('DistanceX',%d,%d,%d,%d,%f)) ",
@@ -2440,7 +2587,7 @@ void CmdSketcherConstrainDistance::applyConstraint(std::vector<SelIdPair> &selSe
                 Obj->getNameInDocument(),GeoId1,PosId1,GeoId2,PosId2,(pnt2-pnt1).Length());
         }
 
-        if (checkBothExternalOrConstructionPoints(Obj,GeoId1, GeoId2) || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
+        if (arebothpointsorsegmentsfixed || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
             const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
 
             Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -2457,6 +2604,8 @@ void CmdSketcherConstrainDistance::applyConstraint(std::vector<SelIdPair> &selSe
     {
         GeoId1 = GeoId2 = selSeq.at(0).GeoId;
         PosId1 = Sketcher::start; PosId2 = Sketcher::end;
+	
+	arebothpointsorsegmentsfixed=isPointOrSegmentFixed(Obj,GeoId1);
 
         const Part::Geometry *geom = Obj->getGeometry(GeoId1);
         if (geom->getTypeId() == Part::GeomLineSegment::getClassTypeId()) {
@@ -2469,7 +2618,7 @@ void CmdSketcherConstrainDistance::applyConstraint(std::vector<SelIdPair> &selSe
                 Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('Distance',%d,%f)) ",
                 Obj->getNameInDocument(),GeoId1,ActLength);
 
-            if (GeoId1 <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId1) || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
+            if (arebothpointsorsegmentsfixed || GeoId1 <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId1) || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
                 const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
 
                 Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -2493,7 +2642,7 @@ void CmdSketcherConstrainDistance::applyConstraint(std::vector<SelIdPair> &selSe
     {
         GeoId1 = selSeq.at(0).GeoId; GeoId2 = selSeq.at(1).GeoId;
         PosId1 = selSeq.at(0).PosId; PosId2 = selSeq.at(1).PosId;
-
+	
         Base::Vector3d pnt = Obj->getPoint(GeoId1,PosId1);
         const Part::Geometry *geom = Obj->getGeometry(GeoId2);
         if (geom->getTypeId() == Part::GeomLineSegment::getClassTypeId()) {
@@ -2509,7 +2658,7 @@ void CmdSketcherConstrainDistance::applyConstraint(std::vector<SelIdPair> &selSe
                 Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('Distance',%d,%d,%d,%f)) ",
                 Obj->getNameInDocument(),GeoId1,PosId1,GeoId2,ActDist);
 
-            if (checkBothExternalOrConstructionPoints(Obj,GeoId1, GeoId2) || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
+            if (arebothpointsorsegmentsfixed || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
                 const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
 
                 Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -2663,8 +2812,8 @@ void CmdSketcherConstrainPointOnObject::activated(int iMsg)
         int cnt = 0;
         for (std::size_t iPnt = 0;  iPnt < points.size();  iPnt++) {
             for (std::size_t iCrv = 0;  iCrv < curves.size();  iCrv++) {
-                if (checkBothExternalOrConstructionPoints(Obj, points[iPnt].GeoId, curves[iCrv].GeoId)){
-                    showNoConstraintBetweenExternal();
+                if (areBothPointsOrSegmentsFixed(Obj, points[iPnt].GeoId, curves[iCrv].GeoId)){
+                    showNoConstraintBetweenFixedGeometry();
                     continue;
                 }
                 if (points[iPnt].GeoId == curves[iCrv].GeoId)
@@ -2732,8 +2881,9 @@ void CmdSketcherConstrainPointOnObject::applyConstraint(std::vector<SelIdPair> &
 
     openCommand("add point on object constraint");
     bool allOK = true;
-    if (checkBothExternalOrConstructionPoints(Obj, GeoIdVt, GeoIdCrv)){
-        showNoConstraintBetweenExternal();
+
+    if (areBothPointsOrSegmentsFixed(Obj, GeoIdVt, GeoIdCrv)){
+        showNoConstraintBetweenFixedGeometry();
         allOK = false;
     }
     if (GeoIdVt == GeoIdCrv)
@@ -2750,7 +2900,6 @@ void CmdSketcherConstrainPointOnObject::applyConstraint(std::vector<SelIdPair> &
         return;
     }
 
-
     if (allOK) {
         Gui::Command::doCommand(
                 Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('PointOnObject',%d,%d,%d)) ",
@@ -2840,7 +2989,7 @@ void CmdSketcherConstrainDistanceX::activated(int iMsg)
     if (SubNames.size() == 2)
         getIdsFromName(SubNames[1], Obj, GeoId2, PosId2);
 
-    bool bothexternalorconstructionpoints=checkBothExternalOrConstructionPoints(Obj,GeoId1, GeoId2);
+    bool arebothpointsorsegmentsfixed=areBothPointsOrSegmentsFixed(Obj,GeoId1, GeoId2);
 
     if (GeoId2 == Sketcher::GeoEnum::HAxis || GeoId2 == Sketcher::GeoEnum::VAxis) {
         std::swap(GeoId1,GeoId2);
@@ -2860,6 +3009,8 @@ void CmdSketcherConstrainDistanceX::activated(int iMsg)
                             QObject::tr("Cannot add a horizontal length constraint on an axis!"));
             return;
         }
+        
+        arebothpointsorsegmentsfixed = isPointOrSegmentFixed(Obj,GeoId1);
 
         const Part::Geometry *geom = Obj->getGeometry(GeoId1);
         if (geom->getTypeId() == Part::GeomLineSegment::getClassTypeId()) {
@@ -2888,7 +3039,7 @@ void CmdSketcherConstrainDistanceX::activated(int iMsg)
             Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('DistanceX',%d,%d,%d,%d,%f)) ",
             selection[0].getFeatName(),GeoId1,PosId1,GeoId2,PosId2,ActLength);
 
-        if (bothexternalorconstructionpoints || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
+        if (arebothpointsorsegmentsfixed || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
             const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
             
             Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -2910,13 +3061,16 @@ void CmdSketcherConstrainDistanceX::activated(int iMsg)
 
         Base::Vector3d pnt = Obj->getPoint(GeoId1,PosId1);
         double ActX = pnt.x;
+	
+	arebothpointsorsegmentsfixed=isPointOrSegmentFixed(Obj,GeoId1);
 
         openCommand("add fixed x-coordinate constraint");
         Gui::Command::doCommand(
             Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('DistanceX',%d,%d,%f)) ",
             selection[0].getFeatName(),GeoId1,PosId1,ActX);
         
-        if (GeoId1 <= Sketcher::GeoEnum::RefExt || isConstructionPoint(Obj,GeoId1) || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
+	
+        if (arebothpointsorsegmentsfixed || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
             const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
             
             Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -2986,7 +3140,7 @@ void CmdSketcherConstrainDistanceX::applyConstraint(std::vector<SelIdPair> &selS
         Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('DistanceX',%d,%d,%d,%d,%f)) ",
         Obj->getNameInDocument(),GeoId1,PosId1,GeoId2,PosId2,ActLength);
 
-    if (checkBothExternalOrConstructionPoints(Obj,GeoId1, GeoId2) || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
+    if (areBothPointsOrSegmentsFixed(Obj,GeoId1, GeoId2) || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
         const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
 
         Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -3084,7 +3238,7 @@ void CmdSketcherConstrainDistanceY::activated(int iMsg)
     if (SubNames.size() == 2)
         getIdsFromName(SubNames[1], Obj, GeoId2, PosId2);
 
-    bool bothexternalorconstruction=checkBothExternalOrConstructionPoints(Obj,GeoId1, GeoId2);
+    bool arebothpointsorsegmentsfixed=areBothPointsOrSegmentsFixed(Obj,GeoId1, GeoId2);
     
     if (GeoId2 == Sketcher::GeoEnum::HAxis || GeoId2 == Sketcher::GeoEnum::VAxis) {
         std::swap(GeoId1,GeoId2);
@@ -3102,6 +3256,8 @@ void CmdSketcherConstrainDistanceY::activated(int iMsg)
                         QObject::tr("Cannot add a vertical length constraint on an axis!"));
             return;
         }
+        
+        arebothpointsorsegmentsfixed = isPointOrSegmentFixed(Obj,GeoId1);
 
         const Part::Geometry *geom = Obj->getGeometry(GeoId1);
         if (geom->getTypeId() == Part::GeomLineSegment::getClassTypeId()) {
@@ -3131,7 +3287,7 @@ void CmdSketcherConstrainDistanceY::activated(int iMsg)
             Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('DistanceY',%d,%d,%d,%d,%f)) ",
             selection[0].getFeatName(),GeoId1,PosId1,GeoId2,PosId2,ActLength);
 
-        if (bothexternalorconstruction || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
+        if (arebothpointsorsegmentsfixed || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
             const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
             
             Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -3153,6 +3309,8 @@ void CmdSketcherConstrainDistanceY::activated(int iMsg)
 
         Base::Vector3d pnt = Obj->getPoint(GeoId1,PosId1);
         double ActY = pnt.y;
+	
+	arebothpointsorsegmentsfixed=isPointOrSegmentFixed(Obj,GeoId1);
 
         openCommand("add fixed y-coordinate constraint");
         Gui::Command::doCommand(
@@ -3229,7 +3387,7 @@ void CmdSketcherConstrainDistanceY::applyConstraint(std::vector<SelIdPair> &selS
         Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('DistanceY',%d,%d,%d,%d,%f)) ",
         Obj->getNameInDocument(),GeoId1,PosId1,GeoId2,PosId2,ActLength);
 
-    if (checkBothExternalOrConstructionPoints(Obj,GeoId1, GeoId2) || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
+    if (areBothPointsOrSegmentsFixed(Obj,GeoId1, GeoId2) || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
         const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
 
         Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -3374,9 +3532,9 @@ void CmdSketcherConstrainParallel::activated(int iMsg)
                                  QObject::tr("Select a valid line"));
             return;
         }
-        else if (GeoId < 0) {
+        else if (isPointOrSegmentFixed(Obj,GeoId)) {
             if (hasAlreadyExternal) {
-                showNoConstraintBetweenExternal();
+                showNoConstraintBetweenFixedGeometry();
                 return;
             }
             else
@@ -3429,6 +3587,11 @@ void CmdSketcherConstrainParallel::applyConstraint(std::vector<SelIdPair> &selSe
                                 QObject::tr("The selected edge is not a valid line"));
             return;
         }
+        
+        if( areBothPointsOrSegmentsFixed(Obj,GeoId1, GeoId2)) {
+	    showNoConstraintBetweenFixedGeometry();
+	    return;
+	}
 
         // undo command open
         openCommand("add parallel constraint");
@@ -3571,8 +3734,8 @@ void CmdSketcherConstrainPerpendicular::activated(int iMsg)
     getIdsFromName(SubNames[0], Obj, GeoId1, PosId1);
     getIdsFromName(SubNames[1], Obj, GeoId2, PosId2);
 
-    if (checkBothExternal(GeoId1, GeoId2)) { //checkBothExternal displays error message
-        showNoConstraintBetweenExternal();
+    if (areBothPointsOrSegmentsFixed(Obj, GeoId1, GeoId2)) { //checkBothExternal displays error message
+        showNoConstraintBetweenFixedGeometry();
         return;
     }
 
@@ -3869,6 +4032,12 @@ void CmdSketcherConstrainPerpendicular::applyConstraint(std::vector<SelIdPair> &
     int GeoId1 = Constraint::GeoUndef, GeoId2 = Constraint::GeoUndef, GeoId3 = Constraint::GeoUndef;
     Sketcher::PointPos PosId1 = Sketcher::none, PosId2 = Sketcher::none, PosId3 = Sketcher::none;
 
+    // check if the edge has already a Blocked constraint
+    if ( areBothPointsOrSegmentsFixed(Obj,GeoId1,GeoId2) ) {
+      showNoConstraintBetweenFixedGeometry();    
+      return;
+    }
+    
     switch (seqIndex) {
     case 0: // {SelEdge, SelEdgeOrAxis}
     case 1: // {SelEdgeOrAxis, SelEdge}
@@ -4185,8 +4354,8 @@ void CmdSketcherConstrainTangent::activated(int iMsg)
     getIdsFromName(SubNames[0], Obj, GeoId1, PosId1);
     getIdsFromName(SubNames[1], Obj, GeoId2, PosId2);
 
-    if (checkBothExternal(GeoId1, GeoId2)){ //checkBothExternal displays error message
-        showNoConstraintBetweenExternal();
+    if (areBothPointsOrSegmentsFixed(Obj, GeoId1, GeoId2)){ //checkBothExternal displays error message
+        showNoConstraintBetweenFixedGeometry();
         return;
     }
     if (SubNames.size() == 3) { //tangent via point
@@ -4449,6 +4618,12 @@ void CmdSketcherConstrainTangent::applyConstraint(std::vector<SelIdPair> &selSeq
     int GeoId1 = Constraint::GeoUndef, GeoId2 = Constraint::GeoUndef, GeoId3 = Constraint::GeoUndef;
     Sketcher::PointPos PosId1 = Sketcher::none, PosId2 = Sketcher::none, PosId3 = Sketcher::none;
 
+    // check if the edge has already a Blocked constraint
+    if ( areBothPointsOrSegmentsFixed(Obj,GeoId1,GeoId2) ) {
+      showNoConstraintBetweenFixedGeometry();    
+      return;
+    }
+    
     switch (seqIndex) {
     case 0: // {SelEdge, SelEdgeOrAxis}
     case 1: // {SelEdgeOrAxis, SelEdge}
@@ -4750,34 +4925,44 @@ void CmdSketcherConstrainRadius::activated(int iMsg)
     std::vector< std::pair<int, double> > externalGeoIdRadiusMap;
     
     for (std::vector<std::string>::const_iterator it = SubNames.begin(); it != SubNames.end(); ++it) {
+	bool issegmentfixed = false;
+	int GeoId;
+	
         if (it->size() > 4 && it->substr(0,4) == "Edge") {
-            int GeoId = std::atoi(it->substr(4,4000).c_str()) - 1;
-            const Part::Geometry *geom = Obj->getGeometry(GeoId);
-            if (geom && geom->getTypeId() == Part::GeomArcOfCircle::getClassTypeId()) {
-                const Part::GeomArcOfCircle *arc = static_cast<const Part::GeomArcOfCircle *>(geom);
-                double radius = arc->getRadius();
-                geoIdRadiusMap.push_back(std::make_pair(GeoId, radius));
-            }
-            else if (geom && geom->getTypeId() == Part::GeomCircle::getClassTypeId()) { 
-                const Part::GeomCircle *circle = static_cast<const Part::GeomCircle *>(geom);
-                double radius = circle->getRadius();
-                geoIdRadiusMap.push_back(std::make_pair(GeoId, radius));
-            }
+            GeoId = std::atoi(it->substr(4,4000).c_str()) - 1;
+	    issegmentfixed = isPointOrSegmentFixed(Obj,GeoId);
         }
-        if (it->size() > 4 && it->substr(0,12) == "ExternalEdge") {
-            int GeoId = -std::atoi(it->substr(12,4000).c_str()) - 2;
-            const Part::Geometry *geom = Obj->getGeometry(GeoId);
-            if (geom && geom->getTypeId() == Part::GeomArcOfCircle::getClassTypeId()) {
-                const Part::GeomArcOfCircle *arc = static_cast<const Part::GeomArcOfCircle *>(geom);
-                double radius = arc->getRadius();
-                externalGeoIdRadiusMap.push_back(std::make_pair(GeoId, radius));
-            }
-            else if (geom && geom->getTypeId() == Part::GeomCircle::getClassTypeId()) { 
-                const Part::GeomCircle *circle = static_cast<const Part::GeomCircle *>(geom);
-                double radius = circle->getRadius();
-                externalGeoIdRadiusMap.push_back(std::make_pair(GeoId, radius));
-            }
+        else if (it->size() > 4 && it->substr(0,12) == "ExternalEdge") {
+            GeoId = -std::atoi(it->substr(12,4000).c_str()) - 2;
+	    issegmentfixed = true;
         }
+        else
+	  continue;
+
+	const Part::Geometry *geom = Obj->getGeometry(GeoId);
+	
+	if (geom && geom->getTypeId() == Part::GeomArcOfCircle::getClassTypeId()) {
+	    const Part::GeomArcOfCircle *arc = static_cast<const Part::GeomArcOfCircle *>(geom);
+	    double radius = arc->getRadius();
+	    
+	    if(issegmentfixed) {
+	      externalGeoIdRadiusMap.push_back(std::make_pair(GeoId, radius));
+	    }
+	    else {
+	      geoIdRadiusMap.push_back(std::make_pair(GeoId, radius));
+	    }
+	}
+	else if (geom && geom->getTypeId() == Part::GeomCircle::getClassTypeId()) { 
+	    const Part::GeomCircle *circle = static_cast<const Part::GeomCircle *>(geom);
+	    double radius = circle->getRadius();
+	    
+	    if(issegmentfixed) {
+	      externalGeoIdRadiusMap.push_back(std::make_pair(GeoId, radius));
+	    }
+	    else {
+	      geoIdRadiusMap.push_back(std::make_pair(GeoId, radius));
+	    }
+	}        
     }
 
     if (geoIdRadiusMap.empty() && externalGeoIdRadiusMap.empty()) {
@@ -5031,8 +5216,8 @@ void CmdSketcherConstrainRadius::applyConstraint(std::vector<SelIdPair> &selSeq,
         const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
 
         int indexConstr = ConStr.size() - 1;
-
-        if(GeoId <= Sketcher::GeoEnum::RefExt || constraintCreationMode==Reference) {
+	bool fixed = isPointOrSegmentFixed(Obj,GeoId);
+        if(fixed || constraintCreationMode==Reference) {
             Gui::Command::doCommand(Doc, "App.ActiveDocument.%s.setDriving(%i,%s)",
                                     Obj->getNameInDocument(), ConStr.size()-1, "False");
         }
@@ -5052,7 +5237,7 @@ void CmdSketcherConstrainRadius::applyConstraint(std::vector<SelIdPair> &selSeq,
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         bool show = hGrp->GetBool("ShowDialogOnDistanceConstraint", true);
         // Ask for the value of the radius immediately
-        if (show && constraintCreationMode==Driving && GeoId >= 0) {
+        if (show && constraintCreationMode==Driving && !fixed) {
             QDialog dlg(Gui::getMainWindow());
             Ui::InsertDatum ui_Datum;
             ui_Datum.setupUi(&dlg);
@@ -5241,7 +5426,7 @@ void CmdSketcherConstrainAngle::activated(int iMsg)
             std::swap(PosId2,PosId3);
         };
         
-        bool bothexternal=checkBothExternal(GeoId1, GeoId2);
+        bool bothexternal=areBothPointsOrSegmentsFixed(Obj, GeoId1, GeoId2);
 
         if (isEdge(GeoId1, PosId1) && isEdge(GeoId2, PosId2) && isVertex(GeoId3, PosId3)) {
             double ActAngle = 0.0;
@@ -5296,7 +5481,7 @@ void CmdSketcherConstrainAngle::activated(int iMsg)
 
     } else if (SubNames.size() < 3) {
 
-        bool bothexternal = checkBothExternal(GeoId1, GeoId2);
+        bool bothexternal = areBothPointsOrSegmentsFixed(Obj, GeoId1, GeoId2);
         
         if (isVertex(GeoId1,PosId1) && isEdge(GeoId2,PosId2)) {
             std::swap(GeoId1,GeoId2);
@@ -5549,7 +5734,7 @@ void CmdSketcherConstrainAngle::applyConstraint(std::vector<SelIdPair> &selSeq,
                 Doc,"App.ActiveDocument.%s.addConstraint(Sketcher.Constraint('Angle',%d,%d,%d,%d,%f)) ",
                 Obj->getNameInDocument(),GeoId1,PosId1,GeoId2,PosId2,ActAngle);
 
-            if (checkBothExternal(GeoId1, GeoId2) || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
+            if (areBothPointsOrSegmentsFixed(Obj,GeoId1, GeoId2) || constraintCreationMode==Reference) { // it is a constraint on a external line, make it non-driving
                 const std::vector<Sketcher::Constraint *> &ConStr = Obj->Constraints.getValues();
 
                 Gui::Command::doCommand(Doc,"App.ActiveDocument.%s.setDriving(%i,%s)",
@@ -5586,7 +5771,7 @@ void CmdSketcherConstrainAngle::applyConstraint(std::vector<SelIdPair> &selSeq,
     }
 
 
-    bool bothexternal=checkBothExternal(GeoId1, GeoId2);
+    bool bothexternal=areBothPointsOrSegmentsFixed(Obj,GeoId1, GeoId2);
 
     if (isEdge(GeoId1, PosId1) && isEdge(GeoId2, PosId2) && isVertex(GeoId3, PosId3)) {
         double ActAngle = 0.0;
@@ -5735,14 +5920,14 @@ void CmdSketcherConstrainEqual::activated(int iMsg)
                                  QObject::tr("Select two or more compatible edges"));
             return;
         }
-        else if (GeoId < 0) {
+        else if (isPointOrSegmentFixed(Obj,GeoId)) {
             if (GeoId == Sketcher::GeoEnum::HAxis || GeoId == Sketcher::GeoEnum::VAxis) {
                 QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Wrong selection"),
                                      QObject::tr("Sketch axes cannot be used in equality constraints"));
                 return;
             }
             else if (hasAlreadyExternal) {
-                showNoConstraintBetweenExternal();
+		showNoConstraintBetweenFixedGeometry();    
                 return;
             }
             else
@@ -5811,6 +5996,12 @@ void CmdSketcherConstrainEqual::applyConstraint(std::vector<SelIdPair> &selSeq,
     case 2: // {SelExternalEdge, SelEdge}
     {
         GeoId1 = selSeq.at(0).GeoId; GeoId2 = selSeq.at(1).GeoId;
+	
+	// check if the edge has already a Blocked constraint
+	if ( areBothPointsOrSegmentsFixed(Obj, GeoId1, GeoId2) ) {
+	  showNoConstraintBetweenFixedGeometry();    
+	  return;
+	}
 
         // undo command open
         openCommand("add equality constraint");
@@ -5907,7 +6098,10 @@ void CmdSketcherConstrainSymmetric::activated(int iMsg)
     getIdsFromName(SubNames[1], Obj, GeoId2, PosId2);
 
     if (SubNames.size() == 2) {
-        //checkBothExternal(GeoId1, GeoId2);
+        if ( areBothPointsOrSegmentsFixed(Obj, GeoId1, GeoId2) ) {
+	  showNoConstraintBetweenFixedGeometry();    
+	  return;
+	}
         if (isVertex(GeoId1,PosId1) && isEdge(GeoId2,PosId2)) {
             std::swap(GeoId1,GeoId2);
             std::swap(PosId1,PosId2);
@@ -5954,10 +6148,9 @@ void CmdSketcherConstrainSymmetric::activated(int iMsg)
         std::swap(PosId2,PosId3);
     }
 
-    if ((GeoId1 < 0 && GeoId2 < 0 && GeoId3 < 0)) {
-        QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Wrong selection"),
-            QObject::tr("Cannot add a constraint between external geometries!"));
-        return;
+    if ( areAllPointsOrSegmentsFixed(Obj, GeoId1, GeoId2, GeoId3) ) {
+      showNoConstraintBetweenFixedGeometry();    
+      return;
     }
 
     if (isVertex(GeoId1,PosId1) &&
@@ -6029,6 +6222,11 @@ void CmdSketcherConstrainSymmetric::applyConstraint(std::vector<SelIdPair> &selS
                 QObject::tr("Cannot add a symmetry constraint between a line and its end points!"));
             return;
         }
+        
+        if ( areBothPointsOrSegmentsFixed(Obj, GeoId1, GeoId2) ) {
+	  showNoConstraintBetweenFixedGeometry();    
+	  return;
+	}        
         break;
     }
     case 2: // {SelVertex, SelEdge, SelVertexOrRoot}
@@ -6040,6 +6238,10 @@ void CmdSketcherConstrainSymmetric::applyConstraint(std::vector<SelIdPair> &selS
         GeoId1 = selSeq.at(0).GeoId;  GeoId2 = selSeq.at(2).GeoId; GeoId3 = selSeq.at(1).GeoId;
         PosId1 = selSeq.at(0).PosId;  PosId2 = selSeq.at(2).PosId;
 
+	if ( areAllPointsOrSegmentsFixed(Obj, GeoId1, GeoId2, GeoId3) ) {
+	  showNoConstraintBetweenFixedGeometry();    
+	  return;
+	}
         const Part::Geometry *geom = Obj->getGeometry(GeoId3);
         if (geom->getTypeId() == Part::GeomLineSegment::getClassTypeId()) {
             if (GeoId1 == GeoId2 && GeoId2 == GeoId3) {
@@ -6073,6 +6275,10 @@ void CmdSketcherConstrainSymmetric::applyConstraint(std::vector<SelIdPair> &selS
         GeoId1 = selSeq.at(0).GeoId;  GeoId2 = selSeq.at(2).GeoId; GeoId3 = selSeq.at(1).GeoId;
         PosId1 = selSeq.at(0).PosId;  PosId2 = selSeq.at(2).PosId; PosId3 = selSeq.at(1).PosId;
 
+	if ( areAllPointsOrSegmentsFixed(Obj, GeoId1, GeoId2, GeoId3) ) {
+	  showNoConstraintBetweenFixedGeometry();    
+	  return;
+	}	
         break;
     }
     default:
@@ -6160,8 +6366,8 @@ void CmdSketcherConstrainSnellsLaw::activated(int iMsg)
             std::swap(PosId2,PosId3);
         }
 
-        //a bunch of validity checks
-        if ((GeoId1 < 0 && GeoId2 < 0 && GeoId3 < 0)) {
+        //a bunch of validity checks       
+        if (areAllPointsOrSegmentsFixed(Obj, GeoId1, GeoId2, GeoId3) ) {
             strError = QObject::tr("Can not create constraint with external geometry only!!", dmbg);
             throw(Base::Exception(""));
         }
@@ -6303,7 +6509,7 @@ void CmdSketcherConstrainInternalAlignment::activated(int iMsg)
         Sketcher::PointPos PosId;
         getIdsFromName(*it, Obj, GeoId, PosId);
         
-        if (GeoId < 0) {
+        if (isPointOrSegmentFixed(Obj,GeoId)) {
             if (GeoId == Sketcher::GeoEnum::HAxis || GeoId == Sketcher::GeoEnum::VAxis) {
                 QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Wrong selection"),
                                      QObject::tr("Sketch axes cannot be used in internal alignment constraint"));
diff --git a/src/Mod/Sketcher/Gui/CommandConstraints.h b/src/Mod/Sketcher/Gui/CommandConstraints.h
index 13aebca913..2c7ea14477 100644
--- a/src/Mod/Sketcher/Gui/CommandConstraints.h
+++ b/src/Mod/Sketcher/Gui/CommandConstraints.h
@@ -33,6 +33,12 @@ bool checkBothExternal(int GeoId1, int GeoId2);
 
 bool checkBothExternalOrConstructionPoints(const Sketcher::SketchObject* Obj,int GeoId1, int GeoId2);
 
+bool isPointOrSegmentFixed(const Sketcher::SketchObject* Obj, int GeoId);
+
+bool areBothPointsOrSegmentsFixed(const Sketcher::SketchObject* Obj, int GeoId1, int GeoId2);
+
+bool areAllPointsOrSegmentsFixed(const Sketcher::SketchObject* Obj, int GeoId1, int GeoId2, int GeoId3);
+
 void getIdsFromName(const std::string &name, const Sketcher::SketchObject* Obj, int &GeoId, Sketcher::PointPos &PosId);
 
 bool inline isVertex(int GeoId, Sketcher::PointPos PosId);
@@ -109,6 +115,9 @@ bool tryAutoRecompute();
 /// This function tries to auto-recompute as tryAutoRecompute. If tryAutoRecompute
 /// is not enabled, then it solves the SketchObject.
 void tryAutoRecomputeIfNotSolve(Sketcher::SketchObject* obj);
+
+/// Checks whether there is a constraint of the given type with a First element geoid and a FirstPos PosId
+bool checkConstraint(const std::vector< Sketcher::Constraint * > &vals, Sketcher::ConstraintType type, int geoid, Sketcher::PointPos pos);
 }
 #endif // SKETCHERGUI_DrawSketchHandler_H