diff --git a/lib/class.js b/lib/class.js
index f5d17f0..f038213 100644
--- a/lib/class.js
+++ b/lib/class.js
@@ -63,7 +63,7 @@ exports.abstractMethod = function( definition )
         throw new Error( "Cannot call abstract method" );
     };
 
-    method.abstractFlag = true;
+    define_secure_prop( method, 'abstractFlag', true );
     return method;
 }