diff --git a/System/FilePath/Internal.hs b/System/FilePath/Internal.hs
index 27b73a056d9d229b4a86fa412dc8ba35a87d4115..f0d79d8398603dcb3810a188e1ed35a39602e3c8 100644
--- a/System/FilePath/Internal.hs
+++ b/System/FilePath/Internal.hs
@@ -963,7 +963,7 @@ normalise filepath =
            then singleton _period
            else joinDrive d p
 
-    addPathSeparator = isDirPath filepath
+    addPathSeparator = isDirPath pth
       && not (hasTrailingPathSeparator result)
       && not (isRelativeDrive drv)