diff --git a/servant-server/src/Servant/Server/Utils/CustomCombinators.hs b/servant-server/src/Servant/Server/Utils/CustomCombinators.hs
index 7e82c61a..9f8b34a4 100644
--- a/servant-server/src/Servant/Server/Utils/CustomCombinators.hs
+++ b/servant-server/src/Servant/Server/Utils/CustomCombinators.hs
@@ -19,6 +19,7 @@ module Servant.Server.Utils.CustomCombinators (
 ) where
 
 import           Control.Monad.IO.Class
+import           Control.Exception (throwIO, ErrorCall(..))
 import           Data.ByteString
 import           Data.Proxy
 import           Data.Text
@@ -36,6 +37,7 @@ data CombinatorImplementation combinator arg api context where
     -> Router' env RoutingApplication)
     -> CombinatorImplementation combinator arg api context
 
+-- fixme: get rid of WithArg?
 type family WithArg arg rest where
   WithArg () rest = rest
   WithArg arg rest = arg -> rest
@@ -66,7 +68,8 @@ makeRequestCheckCombinator ::
   -> CombinatorImplementation combinator () api context
 makeRequestCheckCombinator check = CI $ \ Proxy context delayed ->
   route (Proxy :: Proxy api) context $ addMethodCheck delayed $
-  withRequest $ \ request -> liftRouteResult =<< liftIO (check request)
+  withRequest $ \ request ->
+    liftRouteResult =<< liftIO (check (protectBody "makeRequestCheckCombinator" request))
 
 makeAuthCombinator ::
   forall api combinator arg context .
@@ -76,7 +79,8 @@ makeAuthCombinator ::
   -> CombinatorImplementation combinator arg api context
 makeAuthCombinator authCheck = CI $ \ Proxy context delayed ->
   route (Proxy :: Proxy api) context $ addAuthCheck delayed $
-  withRequest $ \ request -> liftRouteResult =<< liftIO (authCheck request)
+  withRequest $ \ request ->
+    liftRouteResult =<< liftIO (authCheck (protectBody "makeAuthCombinator" request))
 
 makeReqBodyCombinator ::
   forall api combinator arg context .
@@ -88,7 +92,8 @@ makeReqBodyCombinator ::
 makeReqBodyCombinator getArg = CI $ \ Proxy context delayed ->
   route (Proxy :: Proxy api) context $ addBodyCheck delayed
   (return ())
-  (\ () -> withRequest $ \ request -> liftRouteResult $ Route $ getArg $ requestBody request)
+  (\ () -> withRequest $ \ request ->
+    liftRouteResult $ Route $ getArg $ requestBody request)
 
 makeCombinator ::
   forall api combinator arg context .
@@ -100,4 +105,11 @@ makeCombinator ::
 makeCombinator getArg = CI $ \ Proxy context delayed ->
   route (Proxy :: Proxy api) context $ addBodyCheck delayed
   (return ())
-  (\ () -> withRequest $ \ request -> liftRouteResult =<< liftIO (getArg request))
+  (\ () -> withRequest $ \ request ->
+    liftRouteResult =<< liftIO (getArg (protectBody "makeCombinator" request)))
+
+protectBody :: String -> Request -> Request
+protectBody name request = request{
+  requestBody = throwIO $ ErrorCall $
+    "ERROR: " ++ name ++ ": combinator must not access the request body"
+}
diff --git a/servant-server/test/Servant/Server/Utils/CustomCombinatorsSpec.hs b/servant-server/test/Servant/Server/Utils/CustomCombinatorsSpec.hs
index d28b27a1..754280fb 100644
--- a/servant-server/test/Servant/Server/Utils/CustomCombinatorsSpec.hs
+++ b/servant-server/test/Servant/Server/Utils/CustomCombinatorsSpec.hs
@@ -86,7 +86,6 @@ spec = do
     responseStatus response `shouldBe` ok200
     responseBodyLbs response `shouldReturn` "\"Alice\""
 
-  -- fixme: rename
   it "allows to write a combinator by providing a function (Request -> a)" $ do
     let server = return
         app = serve (Proxy :: Proxy (FooHeader :> Get' String)) server
@@ -108,14 +107,6 @@ spec = do
                 chunk <- a
                 return (r, chunk)
               [] -> return ([], "")
-        fromBody :: IO SBS.ByteString -> IO SBS.ByteString
-        fromBody getChunk = do
-          chunk <- getChunk
-          if chunk == ""
-            then return ""
-            else do
-              rest <- fromBody getChunk
-              return $ chunk <> rest
 
     it "allows to write combinators" $ do
       body <- toBody $ map return ["foo", "bar"]
@@ -152,11 +143,21 @@ spec = do
     response <- runApp app request
     responseStatus response `shouldBe` status418
 
-  it "allows to pick the request check phase" $ do
-    pending
-
   it "disallows to access the request body unless in the checkBody phase" $ do
-    pending
+    let server = return ()
+        app = serve (Proxy :: Proxy (InvalidRequestCheckCombinator :> Get' ())) server
+        request = defaultRequest
+    runApp app request `shouldThrow`
+      errorCall "ERROR: makeRequestCheckCombinator: combinator must not access the request body"
+
+  it "disallows to access the request body unless in the auth phase" $ do
+    let server _user = return "foo"
+        app = serve (Proxy :: Proxy (InvalidAuthCombinator :> Get' String)) server
+        request = defaultRequest
+    runApp app request `shouldThrow`
+      errorCall "ERROR: makeAuthCombinator: combinator must not access the request body"
+
+  -- fixme: reorder tests
 
   it "allows to access the context" $ do
     pending
@@ -228,3 +229,36 @@ instance HasServer api context => HasServer (StreamRequest :> api) context where
 
 getSource :: IO SBS.ByteString -> Source
 getSource = Source
+
+-- | a combinator that tries to access the request body in an invalid way
+data InvalidRequestCheckCombinator
+
+instance HasServer api context => HasServer (InvalidRequestCheckCombinator :> api) context where
+  type ServerT (InvalidRequestCheckCombinator :> api) m = ServerT api m
+  route = runCI $ makeRequestCheckCombinator accessReqBody
+
+accessReqBody :: Request -> IO (RouteResult ())
+accessReqBody request = do
+  body <- fromBody $ requestBody request
+  deepseq body (return $ Route ())
+
+-- | a combinator that tries to access the request body in an invalid way
+data InvalidAuthCombinator
+
+instance HasServer api context => HasServer (InvalidAuthCombinator :> api) context where
+  type ServerT (InvalidAuthCombinator :> api) m = User -> ServerT api m
+  route = runCI $ makeAuthCombinator authWithReqBody
+
+authWithReqBody :: Request -> IO (RouteResult User)
+authWithReqBody request = do
+  body <- fromBody $ requestBody request
+  deepseq body (return $ Route $ User $ cs body)
+
+fromBody :: IO SBS.ByteString -> IO SBS.ByteString
+fromBody getChunk = do
+  chunk <- getChunk
+  if chunk == ""
+    then return ""
+    else do
+      rest <- fromBody getChunk
+      return $ chunk <> rest