diff --git a/src/org/rascalmpl/library/util/Reflective.rsc b/src/org/rascalmpl/library/util/Reflective.rsc
index 317b37e9000..240847392b9 100644
--- a/src/org/rascalmpl/library/util/Reflective.rsc
+++ b/src/org/rascalmpl/library/util/Reflective.rsc
@@ -142,7 +142,7 @@ tuple[str,str] splitFileExtension(str path){
 str getModuleName(loc moduleLoc,  PathConfig pcfg){
     modulePath = moduleLoc.path;
     
-    if(!(moduleLoc.extension in {"rsc", "tpl"})){
+    if(moduleLoc.extension notin {"rsc", "tpl"}){
         throw "Not a Rascal source or tpl file: <moduleLoc>";
     }