diff --git a/serverless-haskell.cabal b/serverless-haskell.cabal
--- a/serverless-haskell.cabal
+++ b/serverless-haskell.cabal
@@ -4,10 +4,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: eb3183c0aeb30569bc69a5ef32f4f467d305108dd464c3f86d33b56507b3af46
+-- hash: 137eaceeb74935a6ac010d0b06486fde175ceedf641d181bd0371d6579587d5d
 
 name:           serverless-haskell
-version:        0.12.2
+version:        0.12.3
 synopsis:       Deploying Haskell code onto AWS Lambda using Serverless
 description:    Utilities to help process the events from AWS Lambda when deployed with the serverless-haskell plugin.
 category:       AWS, Cloud, Network
diff --git a/src/AWSLambda/Handler.hs b/src/AWSLambda/Handler.hs
--- a/src/AWSLambda/Handler.hs
+++ b/src/AWSLambda/Handler.hs
@@ -115,12 +115,17 @@
         resultOrError <- tryAny $ act input
         case resultOrError of
           Right result   -> liftIO $ void $ httpNoBody (resultRequest address requestId result) manager
-          Left exception -> liftIO $ void $ httpNoBody (errorRequest address requestId exception) manager
+          Left exception -> do
+            putStrLnLBS $ Aeson.encode $ exceptionJSON exception
+            liftIO $ void $ httpNoBody (errorRequest address requestId exception) manager
     Nothing -> do
       input <- liftIO $ LBS.fromStrict <$> ByteString.getLine
       result <- act input
-      liftIO $ Text.putStrLn $ Text.decodeUtf8 $ LBS.toStrict result
+      putStrLnLBS result
 
+putStrLnLBS :: MonadIO m => LBS.ByteString -> m ()
+putStrLnLBS = liftIO . Text.putStrLn . Text.decodeUtf8 . LBS.toStrict
+
 lambdaApiAddressEnv :: String
 lambdaApiAddressEnv = "AWS_LAMBDA_RUNTIME_API"
 
@@ -136,7 +141,10 @@
 errorRequest :: String -> String -> SomeException -> Request
 errorRequest apiAddress requestId exception = (lambdaRequest apiAddress $ "/runtime/invocation/" ++ requestId ++ "/error") { method = "POST", requestBody = RequestBodyLBS body }
   where
-    body = Aeson.encode $ Aeson.object [ "errorMessage" .= displayException exception, "errorType" .= exceptionType exception]
+    body = Aeson.encode $ exceptionJSON exception
+
+exceptionJSON :: SomeException -> Aeson.Value
+exceptionJSON exception = Aeson.object [ "errorMessage" .= displayException exception, "errorType" .= exceptionType exception]
 
 exceptionType :: SomeException -> String
 exceptionType (SomeException e) = show (typeOf e)