diff --git a/src/Mod/Sketcher/App/planegcs/GCS.cpp b/src/Mod/Sketcher/App/planegcs/GCS.cpp
index 474024adca..5dde956f38 100644
--- a/src/Mod/Sketcher/App/planegcs/GCS.cpp
+++ b/src/Mod/Sketcher/App/planegcs/GCS.cpp
@@ -501,6 +501,14 @@ int System::addConstraintEqual(double *param1, double *param2, int tagId, bool d
     return addConstraint(constr);
 }
 
+int System::addConstraintProportional(double *param1, double *param2, double ratio, int tagId, bool driving)
+{
+    Constraint *constr = new ConstraintEqual(param1, param2, ratio);
+    constr->setTag(tagId);
+    constr->setDriving(driving);
+    return addConstraint(constr);
+}
+
 int System::addConstraintDifference(double *param1, double *param2,
                                     double *difference, int tagId, bool driving)
 {
@@ -872,6 +880,16 @@ int System::addConstraintArcRadius(Arc &a, double *radius, int tagId, bool drivi
     return addConstraintEqual(a.rad, radius, tagId, driving);
 }
 
+int System::addConstraintCircleDiameter(Circle &c, double *radius, int tagId, bool driving)
+{
+    return addConstraintProportional(c.rad, radius, 0.5, tagId, driving);
+}
+
+int System::addConstraintArcDiameter(Arc &a, double *radius, int tagId, bool driving)
+{
+    return addConstraintProportional(a.rad, radius, 0.5, tagId, driving);
+}
+
 int System::addConstraintEqualLength(Line &l1, Line &l2, double *length, int tagId, bool driving)
 {
     addConstraintP2PDistance(l1.p1, l1.p2, length, tagId, driving);
diff --git a/src/Mod/Sketcher/App/planegcs/GCS.h b/src/Mod/Sketcher/App/planegcs/GCS.h
index 17d57c8c44..b6d227d683 100644
--- a/src/Mod/Sketcher/App/planegcs/GCS.h
+++ b/src/Mod/Sketcher/App/planegcs/GCS.h
@@ -147,6 +147,7 @@ namespace GCS
 
         // basic constraints
         int addConstraintEqual(double *param1, double *param2, int tagId=0, bool driving = true);
+        int addConstraintProportional(double *param1, double *param2, double ratio, int tagId, bool driving = true);
         int addConstraintDifference(double *param1, double *param2,
                                     double *difference, int tagId=0, bool driving = true);
         int addConstraintP2PDistance(Point &p1, Point &p2, double *distance, int tagId=0, bool driving = true);
@@ -210,6 +211,8 @@ namespace GCS
 
         int addConstraintCircleRadius(Circle &c, double *radius, int tagId=0, bool driving = true);
         int addConstraintArcRadius(Arc &a, double *radius, int tagId=0, bool driving = true);
+        int addConstraintCircleDiameter(Circle &c, double *radius, int tagId=0, bool driving = true);
+        int addConstraintArcDiameter(Arc &a, double *radius, int tagId=0, bool driving = true);
         int addConstraintEqualLength(Line &l1, Line &l2, double *length, int tagId=0, bool driving = true);
         int addConstraintEqualRadius(Circle &c1, Circle &c2, int tagId=0, bool driving = true);
         int addConstraintEqualRadii(Ellipse &e1, Ellipse &e2, int tagId=0, bool driving = true);