diff --git a/src/Mod/Sketcher/App/PropertyConstraintList.cpp b/src/Mod/Sketcher/App/PropertyConstraintList.cpp
index 23cb85040..11d0ab6ab 100644
--- a/src/Mod/Sketcher/App/PropertyConstraintList.cpp
+++ b/src/Mod/Sketcher/App/PropertyConstraintList.cpp
@@ -52,7 +52,7 @@ TYPESYSTEM_SOURCE(Sketcher::PropertyConstraintList, App::PropertyLists);
 // Construction/Destruction
 
 
-PropertyConstraintList::PropertyConstraintList()
+PropertyConstraintList::PropertyConstraintList() : validGeometryKeys(0), invalidGeometry(true)
 {
 
 }
@@ -174,6 +174,9 @@ void PropertyConstraintList::Restore(Base::XMLReader &reader)
 Property *PropertyConstraintList::Copy(void) const
 {
     PropertyConstraintList *p = new PropertyConstraintList();
+    p->setValidGeometryKeys(validGeometryKeys);
+    if (invalidGeometry)
+        p->invalidateGeometry();
     p->setValues(_lValueList);
     return p;
 }
@@ -181,6 +184,9 @@ Property *PropertyConstraintList::Copy(void) const
 void PropertyConstraintList::Paste(const Property &from)
 {
     const PropertyConstraintList& FromList = dynamic_cast<const PropertyConstraintList&>(from);
+    setValidGeometryKeys(FromList.validGeometryKeys);
+    if (FromList.invalidGeometry)
+        invalidateGeometry();
     setValues(FromList._lValueList);
 }
 
@@ -191,3 +197,51 @@ unsigned int PropertyConstraintList::getMemSize(void) const
         size += _lValueList[i]->getMemSize();
     return size;
 }
+
+void PropertyConstraintList::acceptGeometry(const std::vector<Part::Geometry *> &GeoList)
+{
+    aboutToSetValue();
+    validGeometryKeys.clear();
+    validGeometryKeys.reserve(GeoList.size());
+    for (std::vector< Part::Geometry * >::const_iterator it=GeoList.begin();
+         it != GeoList.end(); ++it)
+        validGeometryKeys.push_back((*it)->getTypeId().getKey());
+    invalidGeometry = false;
+    hasSetValue();
+}
+
+void PropertyConstraintList::setValidGeometryKeys(const std::vector<unsigned int> &keys)
+{
+    validGeometryKeys = keys;
+    invalidGeometry = false;
+}
+
+void PropertyConstraintList::invalidateGeometry()
+{
+    invalidGeometry = true;
+}
+
+void PropertyConstraintList::checkGeometry(const std::vector<Part::Geometry *> &GeoList)
+{
+    if (validGeometryKeys.size() != GeoList.size()) {
+        invalidGeometry = true;
+        return;
+    }
+
+    unsigned int i=0;
+    for (std::vector< Part::Geometry * >::const_iterator it=GeoList.begin();
+         it != GeoList.end(); ++it, i++) {
+        if (validGeometryKeys[i] != (*it)->getTypeId().getKey()) {
+            invalidGeometry = true;
+            return;
+        }
+    }
+
+    if (invalidGeometry) {
+        aboutToSetValue();
+        invalidGeometry = false;
+        hasSetValue();
+    }
+}
+
+std::vector<Constraint *> PropertyConstraintList::_emptyValueList(0);
diff --git a/src/Mod/Sketcher/App/PropertyConstraintList.h b/src/Mod/Sketcher/App/PropertyConstraintList.h
index 4843a96f7..54336bf5b 100644
--- a/src/Mod/Sketcher/App/PropertyConstraintList.h
+++ b/src/Mod/Sketcher/App/PropertyConstraintList.h
@@ -30,6 +30,7 @@
 #include <vector>
 #include <string>
 #include <App/Property.h>
+#include <Mod/Part/App/Geometry.h>
 #include "Constraint.h"
 
 namespace Base {
@@ -67,11 +68,11 @@ public:
 
     /// index operator
     const Constraint *operator[] (const int idx) const {
-        return _lValueList[idx];
+        return invalidGeometry ? 0 : _lValueList[idx];
     }
 
     const std::vector<Constraint*> &getValues(void) const {
-        return _lValueList;
+        return invalidGeometry ? _emptyValueList : _lValueList;
     }
 
     virtual PyObject *getPyObject(void);
@@ -85,8 +86,19 @@ public:
 
     virtual unsigned int getMemSize(void) const;
 
+    void acceptGeometry(const std::vector<Part::Geometry *> &GeoList);
+    void invalidateGeometry();
+    void checkGeometry(const std::vector<Part::Geometry *> &GeoList);
+
 private:
-    std::vector<Constraint*> _lValueList;
+    std::vector<Constraint *> _lValueList;
+
+    std::vector<unsigned int> validGeometryKeys;
+    bool invalidGeometry;
+
+    void setValidGeometryKeys(const std::vector<unsigned int> &keys);
+
+    static std::vector<Constraint *> _emptyValueList;
 };
 
 } // namespace Sketcher
diff --git a/src/Mod/Sketcher/App/SketchObject.cpp b/src/Mod/Sketcher/App/SketchObject.cpp
index 0d9cb38b9..3fd949b40 100644
--- a/src/Mod/Sketcher/App/SketchObject.cpp
+++ b/src/Mod/Sketcher/App/SketchObject.cpp
@@ -228,6 +228,7 @@ int SketchObject::addGeometry(const Part::Geometry *geo)
     Part::Geometry *geoNew = geo->clone();
     newVals.push_back(geoNew);
     Geometry.setValues(newVals);
+    Constraints.acceptGeometry(Geometry.getValues());
     delete geoNew;
     rebuildVertexIndex();
     return Geometry.getSize()-1;
@@ -256,13 +257,9 @@ int SketchObject::delGeometry(int GeoNbr)
         }
     }
 
-    // temporarily empty constraints list in order to avoid invalid constraints
-    // during manipulation of the geometry list
-    std::vector< Constraint * > emptyConstraints(0);
-    this->Constraints.setValues(emptyConstraints);
-
     this->Geometry.setValues(newVals);
     this->Constraints.setValues(newConstraints);
+    this->Constraints.acceptGeometry(this->Geometry.getValues());
     rebuildVertexIndex();
     return 0;
 }
@@ -280,6 +277,7 @@ int SketchObject::toggleConstruction(int GeoNbr)
     newVals[GeoNbr]=geoNew;
 
     this->Geometry.setValues(newVals);
+    this->Constraints.acceptGeometry(this->Geometry.getValues());
     return 0;
 }
 
@@ -758,6 +756,8 @@ int SketchObject::trim(int GeoId, const Base::Vector3d& point)
 
             delete newConstr;
 
+            Constraints.acceptGeometry(Geometry.getValues());
+
             return 0;
         }
 
@@ -1066,9 +1066,17 @@ void SketchObject::Restore(XMLReader &reader)
 {
     // read the father classes
     Part::Part2DObject::Restore(reader);
+    Constraints.acceptGeometry(Geometry.getValues());
     rebuildVertexIndex();
 }
 
+void SketchObject::onChanged(const App::Property* prop)
+{
+    if (prop == &Geometry || prop == &Constraints)
+        Constraints.checkGeometry(Geometry.getValues());
+    DocumentObject::onChanged(prop);
+}
+
 void SketchObject::getGeoVertexIndex(int VertexId, int &GeoId, PointPos &PosId)
 {
     if (VertexId < 0 || VertexId >= (int)VertexId2GeoId.size()) {
diff --git a/src/Mod/Sketcher/App/SketchObject.h b/src/Mod/Sketcher/App/SketchObject.h
index 91883ec02..210ee6ae0 100644
--- a/src/Mod/Sketcher/App/SketchObject.h
+++ b/src/Mod/Sketcher/App/SketchObject.h
@@ -44,9 +44,9 @@ public:
     SketchObject();
 
     /// Property
+    Part    ::PropertyGeometryList   Geometry;
     Sketcher::PropertyConstraintList Constraints;
     App     ::PropertyLinkSubList    ExternalConstraints;
-    Part    ::PropertyGeometryList   Geometry;
     /** @name methods overide Feature */
     //@{
     /// recalculate the Feature
@@ -123,6 +123,10 @@ public:
     virtual void Save(Base::Writer &/*writer*/) const;
     virtual void Restore(Base::XMLReader &/*reader*/);
 
+protected:
+    /// get called by the container when a property has changed
+    virtual void onChanged(const App::Property* /*prop*/);
+
 private:
     std::vector<int> VertexId2GeoId;
     std::vector<PointPos> VertexId2PosId;