diff --git a/src/App/PropertyContainer.cpp b/src/App/PropertyContainer.cpp
index 877fbc575d..86052ab416 100644
--- a/src/App/PropertyContainer.cpp
+++ b/src/App/PropertyContainer.cpp
@@ -321,6 +321,7 @@ void PropertyData::addProperty(OffsetBase offsetBase,const char* PropName, Prope
     PropertySpec temp;
     temp.Name   = PropName;
     temp.Offset = offsetBase.getOffsetTo(Prop);
+    assert(temp.Offset>=0);
     temp.Group  = PropertyGroup;
     temp.Type   = Type;
     temp.Docu   = PropertyDocu;
@@ -343,6 +344,8 @@ const PropertyData::PropertySpec *PropertyData::findProperty(OffsetBase offsetBa
 const PropertyData::PropertySpec *PropertyData::findProperty(OffsetBase offsetBase,const Property* prop) const
 {
   const int diff = offsetBase.getOffsetTo(prop);
+  if(diff<0)
+      return 0;
 
   for (vector<PropertyData::PropertySpec>::const_iterator It = propertyData.begin(); It != propertyData.end(); ++It)
     if(diff == It->Offset)
diff --git a/src/App/PropertyContainer.h b/src/App/PropertyContainer.h
index d767af08a8..dab65cc58c 100644
--- a/src/App/PropertyContainer.h
+++ b/src/App/PropertyContainer.h
@@ -25,6 +25,7 @@
 #define APP_PROPERTYCONTAINER_H
 
 #include <map>
+#include <climits>
 #include <Base/Persistence.h>
 
 namespace Base {
@@ -69,7 +70,11 @@ struct AppExport PropertyData
       OffsetBase(const App::Extension* container) : m_container(container) {};
       
       short int getOffsetTo(const App::Property* prop) const {
-            return (short) ((char*)prop - (char*)m_container);
+            auto *pt = (const char*)prop;
+            auto *base = (const char *)m_container;
+            if(pt<base || pt>base+SHRT_MAX)
+                return -1;
+            return (short) (pt-base);
       };
       char* getOffset() const {return (char*) m_container;};