diff --git a/src/Network/GRPC/Client/Session.hs b/src/Network/GRPC/Client/Session.hs
index 53acf715..2ba037d0 100644
--- a/src/Network/GRPC/Client/Session.hs
+++ b/src/Network/GRPC/Client/Session.hs
@@ -88,7 +88,7 @@ instance SupportsClientRpc rpc => InitiateSession (ClientSession rpc) where
   parseResponse (ClientSession conn) (ResponseInfo status headers body) =
       case classifyServerResponse (Proxy @rpc) status headers body of
         Left parsed -> do
-          trailersOnly <- throwSynthesized parsed
+          trailersOnly <- throwSynthesized throwIO parsed
           -- We classify the response as Trailers-Only if the grpc-status header
           -- is present, or when the HTTP status is anything other than 200 OK
           -- (which we treat, as per the spec, as an implicit grpc-status).
@@ -97,7 +97,7 @@ instance SupportsClientRpc rpc => InitiateSession (ClientSession rpc) where
             Left  err   -> throwIO $ CallSetupInvalidResponseHeaders err
             Right _hdrs -> return $ FlowStartNoMessages trailersOnly
         Right parsed -> do
-          responseHeaders <- throwSynthesized parsed
+          responseHeaders <- throwSynthesized throwIO parsed
           case verifyAllIf connVerifyHeaders responseHeaders of
             Left  err  -> throwIO $ CallSetupInvalidResponseHeaders err
             Right hdrs -> do
diff --git a/src/Network/GRPC/Server/Call.hs b/src/Network/GRPC/Server/Call.hs
index ceb4cdfa..bbbdbbfc 100644
--- a/src/Network/GRPC/Server/Call.hs
+++ b/src/Network/GRPC/Server/Call.hs
@@ -190,7 +190,7 @@ determineInbound :: forall rpc.
   -> HTTP2.Request
   -> IO (Headers (ServerInbound rpc), Maybe Timeout)
 determineInbound session req = do
-    requestHeaders' <- throwSynthesized parsed
+    requestHeaders' <- throwSynthesized throwIO parsed
     case verifyAllIf serverVerifyHeaders requestHeaders' of
       Left  err  -> throwIO $ CallSetupInvalidRequestHeaders err
       Right hdrs -> do
diff --git a/src/Network/GRPC/Spec/Headers/Invalid.hs b/src/Network/GRPC/Spec/Headers/Invalid.hs
index 9089b889..7c16f861 100644
--- a/src/Network/GRPC/Spec/Headers/Invalid.hs
+++ b/src/Network/GRPC/Spec/Headers/Invalid.hs
@@ -35,7 +35,6 @@ import Network.HTTP.Types qualified as HTTP
 import Network.GRPC.Spec.Status
 import Network.GRPC.Util.HKD (Checked)
 import Network.GRPC.Util.HKD qualified as HKD
-import Control.Exception
 
 {-------------------------------------------------------------------------------
   Definition
@@ -180,13 +179,14 @@ mapSynthesized :: (e -> e') -> InvalidHeaders e -> InvalidHeaders e'
 mapSynthesized f = runIdentity . mapSynthesizedM (Identity . f)
 
 throwSynthesized ::
-     HKD.Traversable h
-  =>     h (Checked (InvalidHeaders GrpcException))
-  -> IO (h (Checked (InvalidHeaders HandledSynthesized)))
-throwSynthesized =
+     (HKD.Traversable h, Monad m)
+  => (forall a. GrpcException -> m a)
+  ->    h (Checked (InvalidHeaders GrpcException))
+  -> m (h (Checked (InvalidHeaders HandledSynthesized)))
+throwSynthesized throw =
     HKD.traverse $
       either
-        (fmap Left  . mapSynthesizedM throwIO)
+        (fmap Left  . mapSynthesizedM throw)
         (fmap Right . return)
 
 {-------------------------------------------------------------------------------
diff --git a/src/Network/GRPC/Spec/Headers/Response.hs b/src/Network/GRPC/Spec/Headers/Response.hs
index 1a19d5bc..45c32ac1 100644
--- a/src/Network/GRPC/Spec/Headers/Response.hs
+++ b/src/Network/GRPC/Spec/Headers/Response.hs
@@ -27,6 +27,7 @@ module Network.GRPC.Spec.Headers.Response (
   ) where
 
 import Control.Exception
+import Control.Monad.Except (throwError)
 import Data.List.NonEmpty (NonEmpty)
 import Data.Proxy
 import Data.Text (Text)
@@ -273,27 +274,34 @@ data GrpcNormalTermination = GrpcNormalTermination {
 grpcClassifyTermination ::
      ProperTrailers'
   -> Either GrpcException GrpcNormalTermination
-grpcClassifyTermination ProperTrailers {
-                              properTrailersGrpcStatus
-                            , properTrailersGrpcMessage
-                            , properTrailersMetadata
-                            } =
-    case properTrailersGrpcStatus of
-      Right GrpcOk -> Right GrpcNormalTermination {
-          grpcTerminatedMetadata = customMetadataMapToList properTrailersMetadata
-        }
-      Right (GrpcError err) -> Left GrpcException{
-          grpcError         = err
-        , grpcErrorMessage  = case properTrailersGrpcMessage of
-                                Right msg -> msg
-                                Left  _   -> Just "Invalid grpc-message"
-        , grpcErrorMetadata = customMetadataMapToList properTrailersMetadata
-        }
-      Left _invalidStatus -> Left GrpcException {
-          grpcError         = GrpcUnknown
-        , grpcErrorMessage  = Just "Invalid grpc-status"
-        , grpcErrorMetadata = customMetadataMapToList properTrailersMetadata
-        }
+grpcClassifyTermination =
+    -- If there are any synthesized errors, those take precedence
+    either Left aux . throwSynthesized throwError
+  where
+    aux ::
+         ProperTrailers_ (Checked (InvalidHeaders HandledSynthesized))
+      -> Either GrpcException GrpcNormalTermination
+    aux ProperTrailers { properTrailersGrpcStatus
+                       , properTrailersGrpcMessage
+                       , properTrailersMetadata
+                       } =
+        case properTrailersGrpcStatus of
+          Right GrpcOk -> Right GrpcNormalTermination {
+              grpcTerminatedMetadata =
+                customMetadataMapToList properTrailersMetadata
+            }
+          Right (GrpcError err) -> Left GrpcException{
+              grpcError         = err
+            , grpcErrorMessage  = case properTrailersGrpcMessage of
+                                    Right msg -> msg
+                                    Left  _   -> Just "Invalid grpc-message"
+            , grpcErrorMetadata = customMetadataMapToList properTrailersMetadata
+            }
+          Left _invalidStatus -> Left GrpcException {
+              grpcError         = GrpcUnknown
+            , grpcErrorMessage  = Just "Invalid grpc-status"
+            , grpcErrorMetadata = customMetadataMapToList properTrailersMetadata
+            }
 
 -- | Translate gRPC exception to response trailers
 grpcExceptionToTrailers ::  GrpcException -> ProperTrailers
diff --git a/test-grapesy/Test/Driver/ClientServer.hs b/test-grapesy/Test/Driver/ClientServer.hs
index a0eb118d..d9d70bb4 100644
--- a/test-grapesy/Test/Driver/ClientServer.hs
+++ b/test-grapesy/Test/Driver/ClientServer.hs
@@ -446,7 +446,7 @@ withTestServer cfg firstTestFailure handlerLock serverHandlers k = do
               Nothing -> Server.ServerConfig {
                   serverInsecure = Just Server.InsecureConfig {
                       insecureHost = Just "127.0.0.1"
-                    , insecurePort = 50051 -- serverPort cfg
+                    , insecurePort = serverPort cfg
                     }
                 , serverSecure   = Nothing
                 }