diff --git a/src/Mod/Part/App/GeometryDefaultExtension.h b/src/Mod/Part/App/GeometryDefaultExtension.h
index 240b3692e5..d8a2726f69 100644
--- a/src/Mod/Part/App/GeometryDefaultExtension.h
+++ b/src/Mod/Part/App/GeometryDefaultExtension.h
@@ -39,7 +39,7 @@ namespace Part {
         virtual ~GeometryDefaultExtension() = default;
 
         inline void setValue(const T& val) {value = val;};
-        inline const T &getValue() {return value;};
+        inline const T &getValue() const {return value;};
 
         // Persistence implementer ---------------------
         virtual unsigned int getMemSize(void) const;