diff --git a/snap-core.cabal b/snap-core.cabal
--- a/snap-core.cabal
+++ b/snap-core.cabal
@@ -1,5 +1,5 @@
 name:           snap-core
-version:        1.0.3.1
+version:        1.0.3.2
 synopsis:       Snap: A Haskell Web Framework (core interfaces and types)
 
 description:
@@ -35,7 +35,7 @@
 bug-reports:    https://github.com/snapframework/snap-core/issues
 category:       Web, Snap, IO-Streams
 Tested-With:    GHC == 7.4.2, GHC == 7.6.3, GHC == 7.8.4, GHC == 7.10.3,
-                GHC == 8.0.1, GHC == 8.2.1
+                GHC == 8.0.1, GHC == 8.2.1, GHC == 8.4.1
 
 extra-source-files:
   test/TestSuite.hs,
@@ -150,7 +150,7 @@
     time                      >= 1.0     && < 1.9,
     transformers              >= 0.3     && < 0.6,
     transformers-base         >= 0.4     && < 0.5,
-    unix-compat               >= 0.3     && < 0.5,
+    unix-compat               >= 0.3     && < 0.6,
     unordered-containers      >= 0.1.4.3 && < 0.3,
     vector                    >= 0.6     && < 0.13
 
diff --git a/src/Snap/Internal/Parsing.hs b/src/Snap/Internal/Parsing.hs
--- a/src/Snap/Internal/Parsing.hs
+++ b/src/Snap/Internal/Parsing.hs
@@ -23,7 +23,7 @@
 import           Data.Int                         (Int64)
 import           Data.List                        (concat, intercalate, intersperse)
 import           Data.Map                         (Map)
-import qualified Data.Map                         as Map (empty, insertWith', toList)
+import qualified Data.Map                         as Map (empty, insertWith, toList)
 import           Data.Maybe                       (Maybe (..), maybe)
 import           Data.Monoid                      (Monoid (mconcat, mempty), (<>))
 import           Data.Word                        (Word8)
@@ -463,7 +463,7 @@
 
   where
     --------------------------------------------------------------------------
-    ins (!k,v) !m = Map.insertWith' (++) k [v] m
+    ins (!k,v) !m = Map.insertWith (++) k [v] m
 
     --------------------------------------------------------------------------
     parts :: [(ByteString,ByteString)]
diff --git a/src/Snap/Internal/Util/FileUploads.hs b/src/Snap/Internal/Util/FileUploads.hs
--- a/src/Snap/Internal/Util/FileUploads.hs
+++ b/src/Snap/Internal/Util/FileUploads.hs
@@ -79,7 +79,7 @@
 import           Data.Int                         (Int, Int64)
 import qualified Data.IORef                       as IORef
 import           Data.List                        (find, map, (++))
-import qualified Data.Map                         as Map (insertWith')
+import qualified Data.Map                         as Map (insertWith)
 import           Data.Maybe                       (Maybe (..), fromMaybe, isJust, maybe)
 import           Data.Text                        (Text)
 import qualified Data.Text                        as T (concat, pack, unpack)
@@ -411,7 +411,7 @@
         putRequest $ modifyParams (\m -> foldr ins m params) rq
 
     --------------------------------------------------------------------------
-    ins (!k, !v) = Map.insertWith' (\_ ex -> (v:ex)) k [v]
+    ins (!k, !v) = Map.insertWith (\_ ex -> (v:ex)) k [v]
          -- prepend value if key exists, since we are folding from right
 
     --------------------------------------------------------------------------