diff --git a/CHANGES b/CHANGES
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,8 @@
+Version 0.6.4 released 21 Nov 2019
+
+* Data.File.Generic now exports PolyDiff(..) as well as Diff,
+  and we require Diff >= 0.4.  Fixes jgm/gitit#637.
+
 Version 0.6.3.5 released 16 Nov 2019
 
 * Compatibility with Diff-0.4.0 (Galen Huntington).
diff --git a/Data/FileStore/Generic.hs b/Data/FileStore/Generic.hs
--- a/Data/FileStore/Generic.hs
+++ b/Data/FileStore/Generic.hs
@@ -15,6 +15,7 @@
            ( modify
            , create
            , Diff
+           , PolyDiff(..)
            , diff
            , searchRevisions
            , smartRetrieve
@@ -27,11 +28,7 @@
 import Control.Exception as E
 import Data.FileStore.Utils
 import Data.List (isInfixOf)
-import Data.Algorithm.Diff (Diff
-#if MIN_VERSION_Diff(0,4,0)
-  , PolyDiff
-#endif
-  (..), getGroupedDiff)
+import Data.Algorithm.Diff (Diff, PolyDiff (..), getGroupedDiff)
 import System.FilePath ((</>))
 
 handleUnknownError :: E.SomeException -> IO a
diff --git a/filestore.cabal b/filestore.cabal
--- a/filestore.cabal
+++ b/filestore.cabal
@@ -1,5 +1,5 @@
 Name:                filestore
-Version:             0.6.3.5
+Version:             0.6.4
 Cabal-Version:       >= 1.10
 Build-type:          Simple
 Synopsis:            Interface for versioning file stores.
@@ -39,7 +39,7 @@
                          time >= 1.5 && < 1.10,
                          xml >= 1.3 && < 1.4,
                          split >= 0.1 && < 0.3,
-                         Diff >= 0.2 && < 0.5,
+                         Diff >= 0.4 && < 0.5,
                          old-locale >= 1.0 && < 1.1
 
     Exposed-modules:     Data.FileStore, Data.FileStore.Types, Data.FileStore.Git, Data.FileStore.Darcs, Data.FileStore.Mercurial,
@@ -68,7 +68,7 @@
                     HUnit >= 1.2 && < 1.7,
                     mtl,
                     time,
-                    Diff >= 0.2 && < 0.5,
+                    Diff >= 0.4 && < 0.5,
                     filepath >= 1.1 && < 1.5,
                     directory >= 1.1 && < 1.4,
                     filestore