diff --git a/Webperl/Modules.pm b/Webperl/Modules.pm
index 48015db..6dddd80 100644
--- a/Webperl/Modules.pm
+++ b/Webperl/Modules.pm
@@ -158,7 +158,7 @@ sub new_module {
                                     $modrow -> {"args"})
         if($modrow);
 
-    return undef;
+    return $self -> self_error("Request for unknown module '$arg'");
 }