diff --git a/happstack-server.cabal b/happstack-server.cabal
--- a/happstack-server.cabal
+++ b/happstack-server.cabal
@@ -1,5 +1,5 @@
 Name:                happstack-server
-Version:             7.5.0.3
+Version:             7.5.1
 Synopsis:            Web related tools and services.
 Description:         Happstack Server provides an HTTP server and a rich set of functions for routing requests, handling query parameters, generating responses, working with cookies, serving files, and more. For in-depth documentation see the Happstack Crash Course <http://happstack.com/docs/crashcourse/index.html>
 License:             BSD3
@@ -11,7 +11,7 @@
 Build-Type:          Simple
 Cabal-Version:       >= 1.10
 Extra-Source-Files:  tests/Happstack/Server/Tests.hs README.md
-tested-with:         GHC == 7.6.3, GHC == 7.8.4, GHC == 7.10.2, GHC==8.0.1, GHC==8.2.2
+tested-with:         GHC == 7.6.3, GHC == 7.8.4, GHC == 7.10.2, GHC==8.0.1, GHC==8.2.2, GHC==8.4.1
 
 source-repository head
     type:     git
diff --git a/src/Happstack/Server/Internal/Multipart.hs b/src/Happstack/Server/Internal/Multipart.hs
--- a/src/Happstack/Server/Internal/Multipart.hs
+++ b/src/Happstack/Server/Internal/Multipart.hs
@@ -72,11 +72,16 @@
                 -> IO (Bool, Int64 , FilePath)  -- ^ truncated?, saved bytes, saved filename
 
 defaultFileSaver :: FilePath -> Int64 -> FilePath -> ByteString -> IO (Bool, Int64, FilePath)
-defaultFileSaver tmpDir diskQuota filename b =
+defaultFileSaver tmpDir diskQuota filename b
+  | pathSeparator filename = error ("Filename contains path separators: " ++ show filename)
+  | otherwise =
     do (fn, h) <- openBinaryTempFile tmpDir filename
        (trunc, len) <- hPutLimit diskQuota h b
        hClose h
        return (trunc, len, fn)
+ where
+   pathSeparator :: String -> Bool
+   pathSeparator template = any (\x-> x == '/' || x == '\\') template
 
 defaultInputIter :: FileSaver -> FilePath -> Int64 -> Int64 -> Int64 -> Int64 -> Int64 -> Int64 -> Work -> IO InputIter
 defaultInputIter fileSaver tmpDir diskCount ramCount headerCount maxDisk maxRAM maxHeader (BodyWork ctype ps b)