diff --git a/src/App/PropertyFile.h b/src/App/PropertyFile.h
index 3b534e62e4..349bc2e7c5 100644
--- a/src/App/PropertyFile.h
+++ b/src/App/PropertyFile.h
@@ -111,7 +111,7 @@ public:
     std::string getExchangeTempFile(void) const;
     std::string getOriginalFileName(void) const;
 
-    bool isEmpty(void){return _cValue.empty();}
+    bool isEmpty(void) const {return _cValue.empty();}
 
 protected:
     // get the transient path if the property is in a DocumentObject