diff --git a/hashed-storage.cabal b/hashed-storage.cabal
--- a/hashed-storage.cabal
+++ b/hashed-storage.cabal
@@ -1,5 +1,5 @@
 name:          hashed-storage
-version:       0.3.8
+version:       0.3.9
 synopsis:      Hashed file storage support code.
 
 description:   Support code for reading and manipulating hashed file storage
@@ -60,7 +60,7 @@
         Storage.Hashed.Utils
 
     build-depends: base >= 3 && < 5, directory, filepath, bytestring, zlib,
-                   containers, mtl, extensible-exceptions, mmap >= 0.4
+                   containers, mtl, extensible-exceptions, mmap >= 0.4 && < 0.5
 
     c-sources: Bundled/sha2.c