diff --git a/FileCache.hs b/FileCache.hs
--- a/FileCache.hs
+++ b/FileCache.hs
@@ -6,8 +6,8 @@
 import Control.Exception
 import Control.Monad
 import Data.ByteString (ByteString)
-import Data.HashMap (Map)
-import qualified Data.HashMap as M
+import Data.HashMap.Strict (HashMap)
+import qualified Data.HashMap.Strict as M
 import Data.IORef
 import Network.HTTP.Date
 import Network.Wai.Application.Classic
@@ -15,7 +15,7 @@
 import System.Posix.Files
 
 data Entry = Negative | Positive FileInfo
-type Cache = Map ByteString Entry
+type Cache = HashMap ByteString Entry
 type GetInfo = Path -> IO FileInfo
 
 fileInfo :: IORef Cache -> GetInfo
diff --git a/mighttpd2.cabal b/mighttpd2.cabal
--- a/mighttpd2.cabal
+++ b/mighttpd2.cabal
@@ -1,5 +1,5 @@
 Name:                   mighttpd2
-Version:                2.5.5
+Version:                2.5.6
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3
@@ -23,7 +23,6 @@
                       , deepseq
                       , directory
                       , filepath
-                      , hashmap >= 1.2
                       , http-conduit
                       , http-date
                       , http-types
@@ -34,6 +33,7 @@
                       , transformers
                       , unix
                       , unix-bytestring
+                      , unordered-containers
                       , wai >= 1.1
                       , wai-app-file-cgi
                       , wai-logger
@@ -67,7 +67,6 @@
                       , deepseq
                       , directory
                       , filepath
-                      , hashmap >= 1.2 && < 1.3
                       , http-conduit
                       , http-date
                       , http-types
@@ -78,6 +77,7 @@
                       , transformers
                       , unix
                       , unix-bytestring
+                      , unordered-containers
                       , wai >= 1.1
                       , wai-app-file-cgi
                       , wai-logger
