diff --git a/src/Mod/Spreadsheet/App/PropertySheet.h b/src/Mod/Spreadsheet/App/PropertySheet.h
index 7efb01a9d5..54844087e9 100644
--- a/src/Mod/Spreadsheet/App/PropertySheet.h
+++ b/src/Mod/Spreadsheet/App/PropertySheet.h
@@ -182,6 +182,7 @@ protected:
 private:
 
     PropertySheet(const PropertySheet & other);
+    PropertySheet& operator= (const PropertySheet&);
 
     /* friends */