diff --git a/github-webhook-handler.cabal b/github-webhook-handler.cabal
--- a/github-webhook-handler.cabal
+++ b/github-webhook-handler.cabal
@@ -1,5 +1,5 @@
 name:                github-webhook-handler
-version:             0.0.1
+version:             0.0.2
 
 synopsis:            GitHub WebHook Handler
 description:
@@ -18,13 +18,18 @@
 cabal-version:       >=1.10
 
 
+source-repository head
+  type:     git
+  location: git://github.com/wereHamster/github-webhook-handler.git
+
+
 library
   hs-source-dirs:      src
   default-language:    Haskell2010
   ghc-options:         -Wall
 
   build-depends:
-     base >=4.8 && <4.9
+     base >=4 && <4.9
    , bytestring
    , github-types
    , transformers
@@ -32,6 +37,7 @@
    , text
    , vector
    , cryptohash
+   , uuid
 
   exposed-modules:
      GitHub.WebHook.Handler
diff --git a/src/GitHub/WebHook/Handler.hs b/src/GitHub/WebHook/Handler.hs
--- a/src/GitHub/WebHook/Handler.hs
+++ b/src/GitHub/WebHook/Handler.hs
@@ -21,6 +21,8 @@
 import           Data.ByteString
 import qualified Data.ByteString.Char8 as BC8
 
+import           Data.UUID
+
 import           GitHub.Types
 
 
@@ -36,23 +38,41 @@
       -- ^ Action which is used to retrieve a particular header from the
       -- request.
 
-    , hAction :: Either Error Event -> m ()
+    , hAction :: Either Error (UUID, Event) -> m ()
       -- ^ Action which is executed once we've processed all the information
-      -- in the request.
+      -- in the request. GitHub includes a unique UUID in each request.
     }
 
 
 data Error
     = InvalidRequest
+      -- ^ The incoming request is not well-formed. If that happens it means
+      -- GitHub screwed something up, or changed the format of the request.
+
     | ParseError !Text
+      -- ^ The request looks valid but we failed to parse the payload. This
+      -- could be because our parsing code is wrong, or because GitHub added
+      -- a new event type which we don't handle yet.
+
     | UnsignedRequest
+      -- ^ We were expecting a signed request but no signature was included.
+      -- Such requests are rejected beause we don't want to accept requests from
+      -- untrusted sources.
+
     | InvalidSignature
+      -- ^ A signature was included in the request but it did not match the
+      -- secret key which was providid to the handler. Usually points to
+      -- a configuration error on either end.
 
+
 toParseError :: String -> Either Error Event
 toParseError = Left . ParseError . T.pack
 
+
 runHandler :: Monad m => Handler m -> m ()
 runHandler h = do
+    mbDelivery <- return . (fromASCIIBytes =<<) =<< hHeader h "X-GitHub-Delivery"
+
     res <- do
         rawBody     <- hBody h
         mbSignature <- hHeader h "X-Hub-Signature"
@@ -87,4 +107,6 @@
                 Right value -> either toParseError Right $
                     parseEither (eventParser $ decodeUtf8 eventName) value
 
-    hAction h res
+    hAction h $ case mbDelivery of
+        Nothing -> Left InvalidRequest
+        Just uuid -> fmap ((,) uuid) res