diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -1,3 +1,5 @@
+[![Build Status](https://travis-ci.org/tsani/servant-github-webhook.svg?branch=master)](https://travis-ci.org/tsani/servant-github-webhook)
+
 servant-github-webhook
 ======================
 
diff --git a/servant-github-webhook.cabal b/servant-github-webhook.cabal
--- a/servant-github-webhook.cabal
+++ b/servant-github-webhook.cabal
@@ -2,7 +2,7 @@
 -- further documentation, see http://haskell.org/cabal/users-guide/
 
 name:                servant-github-webhook
-version:             0.3.0.1
+version:             0.3.0.2
 synopsis:            Servant combinators to facilitate writing GitHub webhooks.
 description:
   This package provides servant combinators that make writing safe GitHub
@@ -19,7 +19,7 @@
 copyright:           Jacob Thomas Errington 2016
 category:            Web
 build-type:          Simple
-tested-with:         GHC == 8.0.1
+tested-with:         GHC == 7.10.2, GHC == 7.10.3, GHC == 8.0.1
 extra-source-files:
   ChangeLog.md
   README.md
@@ -29,6 +29,10 @@
   type: git
   location: https://github.com/tsani/servant-github-webhook.git
 
+flag old-base
+  description: whether to use base-4.8 and transformers rather than base 4.9
+  default: True
+
 library
   exposed-modules:
     Servant.GitHub.Webhook
@@ -38,18 +42,25 @@
     -Wall
   build-depends:
     aeson >=0.11 && <1.1,
-    base >=4.8 && <4.10,
+    base16-bytestring >=0.1 && <0.2,
     bytestring >= 0.10 && <0.11,
+    Crypto >=4.2 && <4.3,
+    github >=0.15 && <0.16,
     http-types >=0.9 && <0.10,
-    text >=1.2 && <1.3,
     servant >=0.8 && <0.10,
     servant-server >=0.8 && <0.10,
-    github >=0.15 && <0.16,
-    wai >=3.2 && <3.3,
-    Crypto >=4.2 && <4.3,
-    base16-bytestring >=0.1 && <0.2,
-    string-conversions >=0.4 && <0.5
+    string-conversions >=0.4 && <0.5,
+    text >=1.2 && <1.3,
+    wai >=3.2 && <3.3
 
+  if flag(old-base)
+    build-depends:
+      base >=4.8 && <4.9,
+      transformers >=0.2 && <0.6
+  else
+    build-depends:
+      base >=4.9 && <4.10
+
 test-suite multikey
   type:                exitcode-stdio-1.0
   ghc-options:
@@ -66,6 +77,10 @@
     wai,
     warp
 
+  if flag(old-base)
+    build-depends:
+      transformers >=0.2 && <0.6
+
 test-suite singlekey
   type:                exitcode-stdio-1.0
   ghc-options:
@@ -81,3 +96,7 @@
     servant-github-webhook,
     wai,
     warp
+
+  if flag(old-base)
+    build-depends:
+      transformers >=0.2 && <0.6
diff --git a/src/Servant/GitHub/Webhook.hs b/src/Servant/GitHub/Webhook.hs
--- a/src/Servant/GitHub/Webhook.hs
+++ b/src/Servant/GitHub/Webhook.hs
@@ -38,6 +38,8 @@
 retrieve.
 -}
 
+{-# LANGUAGE CPP #-}
+
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FlexibleInstances #-}
@@ -51,6 +53,16 @@
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeOperators #-}
 
+-- GHC 8 seems to have improved its decidability check for type family
+-- instances and class instances. In particular, without UndecidableInstances
+-- enabled, the Demote' instance for lists, which we need, will not compile.
+-- Similarly, the Reflect instance for Symbol, which just requires KnownSymbol,
+-- won't compile on GHC < 8 because the instance head is no smaller than the
+-- instance head.
+#if __GLASGOW_HASKELL__ < 800
+{-# LANGUAGE UndecidableInstances #-}
+#endif
+
 module Servant.GitHub.Webhook
 ( -- * Servant combinators
   GitHubSignedReqBody''
@@ -172,7 +184,7 @@
 -- The type @key@ used here must correspond with @'Demote' k@ where @k@ is the
 -- kind whose types are used as indices in 'GitHubSignedReqBody''.
 --
--- If you don't care about indices and just want to write a webhooks using a
+-- If you don't care about indices and just want to write a webhook using a
 -- global key, see 'GitHubKey' which fixes @key@ to @()@ and use 'gitHubKey',
 -- which fills the newtype with a constant function.
 newtype GitHubKey' key = GitHubKey { unGitHubKey :: key -> IO BS.ByteString }
diff --git a/test/multikey/Main.hs b/test/multikey/Main.hs
--- a/test/multikey/Main.hs
+++ b/test/multikey/Main.hs
@@ -15,8 +15,14 @@
 import Servant
 import Servant.GitHub.Webhook
 
+-- | Entry point for travis.
+-- We don't actually have automated tests, so we use a dummy main for travis,
+-- so that /running/ the tests passes, but compiling may not.
 main :: IO ()
-main = do
+main = pure ()
+
+realMain :: IO ()
+realMain = do
   [k1, k2] <- C8.lines <$> BS.readFile "test/test-keys"
   run 8080 (app (constKeys k1 k2))
 
@@ -26,13 +32,13 @@
 server :: Server WebhookApi
 server = (repo1ping :<|> repo1any) :<|> repo2any
 
-repo1ping :: RepoWebhookEvent -> Object -> Handler ()
+repo1ping :: RepoWebhookEvent -> (Key, Object) -> Handler ()
 repo1ping _ _ = liftIO $ putStrLn "got ping on repo1!"
 
-repo1any :: RepoWebhookEvent -> Object -> Handler ()
+repo1any :: RepoWebhookEvent -> (Key, Object) -> Handler ()
 repo1any e _ = liftIO $ putStrLn $ "got event on repo 1: " ++ show e
 
-repo2any :: RepoWebhookEvent -> Object -> Handler ()
+repo2any :: RepoWebhookEvent -> (Key, Object) -> Handler ()
 repo2any e _ = liftIO $ putStrLn $ "got event on repo 2: " ++ show e
 
 api :: Proxy WebhookApi
@@ -40,19 +46,19 @@
 
 type WebhookApi
   = "repo1" :> (
-      GitHubEvent '[ 'WebhookPingEvent ]
-    :> GitHubSignedReqBody' 'Repo1 '[JSON] Object
-    :> Post '[JSON] ()
-    :<|>
-      GitHubEvent '[ 'WebhookWildcardEvent ]
-    :> GitHubSignedReqBody' 'Repo1 '[JSON] Object
-    :> Post '[JSON] ()
+    GitHubEvent '[ 'WebhookPingEvent ]
+      :> GitHubSignedReqBody' 'Repo1 '[JSON] Object
+      :> Post '[JSON] ()
+  :<|>
+    GitHubEvent '[ 'WebhookWildcardEvent ]
+      :> GitHubSignedReqBody' 'Repo1 '[JSON] Object
+      :> Post '[JSON] ()
   )
   :<|>
     "repo2"
-    :> GitHubEvent '[ 'WebhookWildcardEvent ]
-    :> GitHubSignedReqBody' 'Repo2 '[JSON] Object
-    :> Post '[JSON] ()
+      :> GitHubEvent '[ 'WebhookWildcardEvent ]
+      :> GitHubSignedReqBody' 'Repo2 '[JSON] Object
+      :> Post '[JSON] ()
 
 type MyGitHubKey = GitHubKey' Key
 
diff --git a/test/singlekey/Main.hs b/test/singlekey/Main.hs
--- a/test/singlekey/Main.hs
+++ b/test/singlekey/Main.hs
@@ -12,7 +12,10 @@
 import Network.Wai.Handler.Warp ( run )
 
 main :: IO ()
-main = do
+main = pure ()
+
+realMain :: IO ()
+realMain = do
   [key, _] <- C8.lines <$> BS.readFile "test/test-keys"
   run 8080 (app (gitHubKey $ pure key))
 
@@ -26,7 +29,7 @@
 server :: Server API
 server = anyEvent
 
-anyEvent :: RepoWebhookEvent -> Object -> Handler ()
+anyEvent :: RepoWebhookEvent -> ((), Object) -> Handler ()
 anyEvent e _
   = liftIO $ putStrLn $ "got event: " ++ show e