diff --git a/lib/src/prelude/Prelude.gf b/lib/src/prelude/Prelude.gf
index ab1fccba8..1c5b50354 100644
--- a/lib/src/prelude/Prelude.gf
+++ b/lib/src/prelude/Prelude.gf
@@ -153,5 +153,9 @@ oper
     _ => s
     } ;
 
+-- handling errors caused by temporarily missing definitions
+
+  notYet : Str -> Predef.Error = \s ->
+    Predef.error ("NOT YET IMPLEMENTED:" ++ s) ;
 
 }