diff --git a/lib/interface.js b/lib/interface.js
index c6855cc..7958c80 100644
--- a/lib/interface.js
+++ b/lib/interface.js
@@ -73,7 +73,7 @@ var extend = ( function( extending )
             {
                 throw TypeError(
                     "Properties are not permitted within Interface " +
-                        "definitions"
+                        "definitions (did you forget the 'abstract' keyword?)"
                 );
             },