diff --git a/lib/customisation.nix b/lib/customisation.nix
index 9c50e6a26c3d..c73f2f2911bb 100644
--- a/lib/customisation.nix
+++ b/lib/customisation.nix
@@ -291,7 +291,7 @@ rec {
             if loc != null then
               loc.file + ":" + toString loc.line
             else if !isFunction fn then
-              toString fn + optionalString (pathIsDirectory fn) "/default.nix"
+              toString (lib.filesystem.resolveDefaultNix fn)
             else
               "<unknown location>";
         in