diff --git a/src/Mod/Sketcher/Gui/CommandConstraints.cpp b/src/Mod/Sketcher/Gui/CommandConstraints.cpp
index 2d8569a01e..5b85d231c0 100644
--- a/src/Mod/Sketcher/Gui/CommandConstraints.cpp
+++ b/src/Mod/Sketcher/Gui/CommandConstraints.cpp
@@ -342,7 +342,7 @@ bool SketcherGui::isSimpleVertex(const Sketcher::SketchObject* Obj, int GeoId, P
 bool SketcherGui::isConstructionPoint(const Sketcher::SketchObject* Obj, int GeoId)
 {
     const Part::Geometry * geo = Obj->getGeometry(GeoId);
-    return (geo->getTypeId() == Part::GeomPoint::getClassTypeId() && geo->Construction == true);
+    return (geo && geo->getTypeId() == Part::GeomPoint::getClassTypeId() && geo->Construction == true);
 }
 
 bool SketcherGui::IsPointAlreadyOnCurve(int GeoIdCurve, int GeoIdPoint, Sketcher::PointPos PosIdPoint, Sketcher::SketchObject* Obj)
@@ -1213,14 +1213,14 @@ void CmdSketcherConstrainHorizontal::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         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 an edge from the sketch."));
@@ -1460,7 +1460,7 @@ void CmdSketcherConstrainVertical::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         bool constraintMode = hGrp->GetBool("ContinuousConstraintMode", true);
 
@@ -1706,7 +1706,7 @@ void CmdSketcherConstrainLock::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         bool constraintMode = hGrp->GetBool("ContinuousConstraintMode", true);
 
@@ -1974,7 +1974,7 @@ void CmdSketcherConstrainBlock::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
     
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         bool constraintMode = hGrp->GetBool("ContinuousConstraintMode", true);
         
@@ -2284,7 +2284,7 @@ void CmdSketcherConstrainCoincident::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         bool constraintMode = hGrp->GetBool("ContinuousConstraintMode", true);
 
@@ -2478,7 +2478,7 @@ void CmdSketcherConstrainDistance::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         bool constraintMode = hGrp->GetBool("ContinuousConstraintMode", true);
 
@@ -2862,14 +2862,14 @@ void CmdSketcherConstrainPointOnObject::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         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 {
             // TODO: Get the exact message from git history and put it here
             QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Wrong selection"),
@@ -3046,7 +3046,7 @@ void CmdSketcherConstrainDistanceX::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         bool constraintMode = hGrp->GetBool("ContinuousConstraintMode", true);
 
@@ -3296,14 +3296,14 @@ void CmdSketcherConstrainDistanceY::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         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 {
             // TODO: Get the exact message from git history and put it here
             QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Wrong selection"),
@@ -3581,14 +3581,14 @@ void CmdSketcherConstrainParallel::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         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 {
             // TODO: Get the exact message from git history and put it here
             QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Wrong selection"),
@@ -3789,14 +3789,14 @@ void CmdSketcherConstrainPerpendicular::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         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 {
             // TODO: Get the exact message from git history and put it here
             strError = QObject::tr("Select some geometry from the sketch.", "perpendicular constraint");
@@ -4409,14 +4409,14 @@ void CmdSketcherConstrainTangent::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         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 {
             strError = QObject::tr("Select some geometry from the sketch.", "tangent constraint");
             if (!strError.isEmpty()) strError.append(QString::fromLatin1("\n\n"));
@@ -5002,14 +5002,14 @@ void CmdSketcherConstrainRadius::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         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 {
             // TODO: Get the exact message from git history and put it here
             QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Wrong selection"),
@@ -5473,7 +5473,7 @@ void CmdSketcherConstrainDiameter::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
     
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         bool constraintMode = hGrp->GetBool("ContinuousConstraintMode", true);
         
@@ -6064,14 +6064,14 @@ void CmdSketcherConstrainAngle::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         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 {
             // TODO: Get the exact message from git history and put it here
             QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Wrong selection"),
@@ -6565,7 +6565,7 @@ void CmdSketcherConstrainEqual::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         bool constraintMode = hGrp->GetBool("ContinuousConstraintMode", true);
 
@@ -6763,7 +6763,7 @@ void CmdSketcherConstrainSymmetric::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Mod/Sketcher");
         bool constraintMode = hGrp->GetBool("ContinuousConstraintMode", true);
 
@@ -7032,15 +7032,15 @@ void CmdSketcherConstrainSnellsLaw::activated(int iMsg)
     try{
         // get the selection
         std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
-        Sketcher::SketchObject* Obj = static_cast<Sketcher::SketchObject*>(selection[0].getObject());
 
         // only one sketch with its subelements are allowed to be selected
-        if (selection.size() != 1) {
+        if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
             strError = QObject::tr("Selected objects are not just geometry from one sketch.", dmbg);
             throw(Base::Exception(""));
         }
 
         // get the needed lists and objects
+        Sketcher::SketchObject* Obj = static_cast<Sketcher::SketchObject*>(selection[0].getObject());
         const std::vector<std::string> &SubNames = selection[0].getSubNames();
 
         if (SubNames.size() != 3) {
@@ -7177,7 +7177,7 @@ void CmdSketcherConstrainInternalAlignment::activated(int iMsg)
     std::vector<Gui::SelectionObject> selection = getSelection().getSelectionEx();
 
     // only one sketch with its subelements are allowed to be selected
-    if (selection.size() != 1) {
+    if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
         QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Wrong selection"),
             QObject::tr("Select at least one ellipse and one edge from the sketch."));
         return;
@@ -7612,7 +7612,7 @@ void CmdSketcherToggleDrivingConstraint::activated(int iMsg)
         selection = getSelection().getSelectionEx();
 
         // only one sketch with its subelements are allowed to be selected
-        if (selection.size() != 1) {
+        if (selection.size() != 1 || !selection[0].isObjectTypeOf(Sketcher::SketchObject::getClassTypeId())) {
             QMessageBox::warning(Gui::getMainWindow(), QObject::tr("Wrong selection"),
                 QObject::tr("Select constraint(s) from the sketch."));
             return;