diff --git a/shake-ext.cabal b/shake-ext.cabal
--- a/shake-ext.cabal
+++ b/shake-ext.cabal
@@ -1,5 +1,5 @@
 name:                shake-ext
-version:             0.3.1.1
+version:             0.3.1.2
 synopsis:            Helper functions for linting with shake 
 description:         This package provides several linters out of the box, as well as functionality for building ATS source files with [shake](http://shakebuild.com/).
 homepage:            https://hub.darcs.net/vmchale/shake-ext
diff --git a/src/Development/Shake/Linters.hs b/src/Development/Shake/Linters.hs
--- a/src/Development/Shake/Linters.hs
+++ b/src/Development/Shake/Linters.hs
@@ -9,14 +9,20 @@
                                  , module Development.Shake.FileDetect
                                  ) where
 
+import           Control.Composition
+import           Data.Char                    (isSpace)
 import           Development.Shake
 import           Development.Shake.FileDetect
 
+trim :: String -> String
+trim = join fmap f
+   where f = reverse . dropWhile isSpace
+
 checkIdempotent :: String -> FilePath -> Action ()
 checkIdempotent s p = do
     contents <- liftIO $ readFile p
     (Stdout out) <- cmd (s ++ " " ++ p)
-    if contents == out then pure () else error "formatter is not fully applied!"
+    if trim contents == trim out then pure () else error "formatter is not fully applied!"
 
 atsfmt :: [FilePath] -> Action ()
 atsfmt = mapM_ (checkIdempotent "atsfmt")