diff --git a/Network/Wai/Application/Classic/Field.hs b/Network/Wai/Application/Classic/Field.hs
--- a/Network/Wai/Application/Classic/Field.hs
+++ b/Network/Wai/Application/Classic/Field.hs
@@ -16,7 +16,7 @@
 import Network.Wai
 import Network.Wai.Application.Classic.Header
 import Network.Wai.Application.Classic.Lang
-import Network.Wai.Application.Static (defaultMimeTypes, defaultMimeType, MimeType)
+import Network.Wai.Application.Static (defaultMimeTypes, defaultMimeType, MimeType, fromFilePath)
 
 ----------------------------------------------------------------
 
@@ -61,4 +61,4 @@
     exts = if entire == "" then [] else entire : BS.split 46 file
 
 defaultMimeTypes' :: StaticHash ByteString MimeType
-defaultMimeTypes' = SH.fromList $ map (first BS.pack) $ Map.toList defaultMimeTypes
+defaultMimeTypes' = SH.fromList $ map (first (BS.pack.fromFilePath)) $ Map.toList defaultMimeTypes
diff --git a/wai-app-file-cgi.cabal b/wai-app-file-cgi.cabal
--- a/wai-app-file-cgi.cabal
+++ b/wai-app-file-cgi.cabal
@@ -1,5 +1,5 @@
 Name:                   wai-app-file-cgi
-Version:                0.3.0
+Version:                0.3.1
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3