diff --git a/CHANGES.txt b/CHANGES.txt
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,5 +1,7 @@
 Changelog for Extra
 
+1.4.5
+    #17, change fileEq on files that do not exist to be an error
 1.4.4
     #14, add mconcatMap and mconcatMapM
     #16, add fileEq
diff --git a/Generate.hs b/Generate.hs
--- a/Generate.hs
+++ b/Generate.hs
@@ -75,8 +75,8 @@
 tweakTest x
     | Just x <- stripSuffix " == undefined" x =
         if not $ "\\" `isPrefixOf` x then
-            "erroneous $ " ++ trim x
+            (if "fileEq" `isInfixOf` x then "erroneousIO $ " else "erroneous $ ") ++ trim x
         else
             let (a,b) = breakOn "->" $ trim x
-            in a ++ "-> erroneous $ " ++ drop 2 b
+            in a ++ "-> erroneous $ " ++ trim (drop 2 b)
     | otherwise = x
diff --git a/extra.cabal b/extra.cabal
--- a/extra.cabal
+++ b/extra.cabal
@@ -1,7 +1,7 @@
 cabal-version:      >= 1.10
 build-type:         Simple
 name:               extra
-version:            1.4.4
+version:            1.4.5
 license:            BSD3
 license-file:       LICENSE
 category:           Development
diff --git a/src/System/IO/Extra.hs b/src/System/IO/Extra.hs
--- a/src/System/IO/Extra.hs
+++ b/src/System/IO/Extra.hs
@@ -234,15 +234,15 @@
           withb = allocaBytesAligned bufsz 4096
           bufsz = 64*1024
 
--- | Returs 'True' when both files exist and have the same content.
+-- | Returns 'True' if both files have the same content.
+--   Raises an error if either file is missing.
 --
--- > notM $ fileEq "does_not_exist" "does_not_exist"
+-- > fileEq "does_not_exist1" "does_not_exist2" == undefined
+-- > fileEq "does_not_exist" "does_not_exist" == undefined
+-- > withTempFile $ \f1 -> fileEq "does_not_exist" f1 == undefined
 -- > withTempFile $ \f1 -> withTempFile $ \f2 -> fileEq f1 f2
 -- > withTempFile $ \f1 -> withTempFile $ \f2 -> writeFile f1 "a" >> writeFile f2 "a" >> fileEq f1 f2
 -- > withTempFile $ \f1 -> withTempFile $ \f2 -> writeFile f1 "a" >> writeFile f2 "b" >> notM (fileEq f1 f2)
 fileEq :: FilePath -> FilePath -> IO Bool
-fileEq p1 p2 =
-    doesFileExist p1
-    &&^ doesFileExist p2
-    &&^ withH p1 (\h1 -> withH p2 $ \h2 -> sameContent h1 h2)
+fileEq p1 p2 = withH p1 $ \h1 -> withH p2 $ \h2 -> sameContent h1 h2
     where withH p = withBinaryFile p ReadMode
diff --git a/test/TestGen.hs b/test/TestGen.hs
--- a/test/TestGen.hs
+++ b/test/TestGen.hs
@@ -50,9 +50,9 @@
     testGen "findM (Just . isUpper) \"test\"             == Just Nothing" $ findM (Just . isUpper) "test"             == Just Nothing
     testGen "findM (Just . const True) [\"x\",undefined] == Just (Just \"x\")" $ findM (Just . const True) ["x",undefined] == Just (Just "x")
     testGen "\\x -> fromLeft (Left  x) == x" $ \x -> fromLeft (Left  x) == x
-    testGen "\\x -> fromLeft (Right x) == undefined" $ \x -> erroneous $  fromLeft (Right x)
+    testGen "\\x -> fromLeft (Right x) == undefined" $ \x -> erroneous $ fromLeft (Right x)
     testGen "\\x -> fromRight (Right x) == x" $ \x -> fromRight (Right x) == x
-    testGen "\\x -> fromRight (Left  x) == undefined" $ \x -> erroneous $  fromRight (Left  x)
+    testGen "\\x -> fromRight (Left  x) == undefined" $ \x -> erroneous $ fromRight (Left  x)
     testGen "\\x -> fromEither (Left x ) == x" $ \x -> fromEither (Left x ) == x
     testGen "\\x -> fromEither (Right x) == x" $ \x -> fromEither (Right x) == x
     testGen "\\xs -> repeatedly (splitAt 3) xs  == chunksOf 3 xs" $ \xs -> repeatedly (splitAt 3) xs  == chunksOf 3 xs
@@ -214,7 +214,9 @@
     testGen "withTempDir doesDirectoryExist == return True" $ withTempDir doesDirectoryExist == return True
     testGen "(doesDirectoryExist =<< withTempDir return) == return False" $ (doesDirectoryExist =<< withTempDir return) == return False
     testGen "withTempDir listFiles == return []" $ withTempDir listFiles == return []
-    testGen "notM $ fileEq \"does_not_exist\" \"does_not_exist\"" $ notM $ fileEq "does_not_exist" "does_not_exist"
+    testGen "fileEq \"does_not_exist1\" \"does_not_exist2\" == undefined" $ erroneousIO $ fileEq "does_not_exist1" "does_not_exist2"
+    testGen "fileEq \"does_not_exist\" \"does_not_exist\" == undefined" $ erroneousIO $ fileEq "does_not_exist" "does_not_exist"
+    testGen "withTempFile $ \\f1 -> fileEq \"does_not_exist\" f1 == undefined" $ erroneousIO $ withTempFile $ \f1 -> fileEq "does_not_exist" f1
     testGen "withTempFile $ \\f1 -> withTempFile $ \\f2 -> fileEq f1 f2" $ withTempFile $ \f1 -> withTempFile $ \f2 -> fileEq f1 f2
     testGen "withTempFile $ \\f1 -> withTempFile $ \\f2 -> writeFile f1 \"a\" >> writeFile f2 \"a\" >> fileEq f1 f2" $ withTempFile $ \f1 -> withTempFile $ \f2 -> writeFile f1 "a" >> writeFile f2 "a" >> fileEq f1 f2
     testGen "withTempFile $ \\f1 -> withTempFile $ \\f2 -> writeFile f1 \"a\" >> writeFile f2 \"b\" >> notM (fileEq f1 f2)" $ withTempFile $ \f1 -> withTempFile $ \f2 -> writeFile f1 "a" >> writeFile f2 "b" >> notM (fileEq f1 f2)
diff --git a/test/TestUtil.hs b/test/TestUtil.hs
--- a/test/TestUtil.hs
+++ b/test/TestUtil.hs
@@ -1,6 +1,6 @@
-{-# LANGUAGE ScopedTypeVariables, CPP #-}
+{-# LANGUAGE ScopedTypeVariables, CPP, FlexibleInstances #-}
 
-module TestUtil(runTests, testGen, testRaw, erroneous, (====), module X) where
+module TestUtil(runTests, testGen, testRaw, erroneous, erroneousIO, (====), module X) where
 
 import Test.QuickCheck
 import Test.QuickCheck.Test
@@ -48,6 +48,9 @@
 
 erroneous :: a -> Bool
 erroneous x = unsafePerformIO $ fmap isLeft $ try_ $ evaluate x
+
+erroneousIO :: IO a -> Bool
+erroneousIO x = unsafePerformIO $ fmap isLeft $ try_ $ evaluate =<< x
 
 (====) :: (Show a, Eq a) => a -> a -> Bool
 a ==== b = if a == b then True else error $ "Not equal!\n" ++ show a ++ "\n" ++ show b