diff --git a/shelly.cabal b/shelly.cabal
--- a/shelly.cabal
+++ b/shelly.cabal
@@ -1,6 +1,6 @@
 Name:       shelly
 
-Version:     1.3.0.4
+Version:     1.3.0.5
 Synopsis:    shell-like (systems) programming in Haskell
 
 Description: Shelly provides convenient systems programming in Haskell,
diff --git a/src/Shelly.hs b/src/Shelly.hs
--- a/src/Shelly.hs
+++ b/src/Shelly.hs
@@ -529,7 +529,7 @@
 which :: FilePath -> Sh (Maybe FilePath)
 which originalFp = whichFull
 #if defined(mingw32_HOST_OS)
-    case extension originalFp of
+    $ case extension originalFp of
         Nothing -> originalFp <.> "exe"
         Just _ -> originalFp
 #else