diff --git a/src/main/scala/de/thm/mope/tree/ModelicaProjectTree.scala b/src/main/scala/de/thm/mope/tree/ModelicaProjectTree.scala
index 7708c59..fdb0c5c 100644
--- a/src/main/scala/de/thm/mope/tree/ModelicaProjectTree.scala
+++ b/src/main/scala/de/thm/mope/tree/ModelicaProjectTree.scala
@@ -36,7 +36,7 @@ object ModelicaProjectTree {
 
   def singleFiles(tree: TreeLike[Path], packageDirectories: List[Path]): List[Path] = {
     tree.filterElements { path =>
-      !packageDirectories.forall(path.startsWith)
+      packageDirectories.find(path.startsWith).isEmpty
     }.filterNot(Files.isDirectory(_))
   }
 }