diff --git a/proxy/handler_multi_test.go b/proxy/handler_multi_test.go
index 0168222..36511aa 100644
--- a/proxy/handler_multi_test.go
+++ b/proxy/handler_multi_test.go
@@ -73,7 +73,7 @@ func (s *assertingMultiService) Ping(ctx context.Context, ping *pb.PingRequest)
 	}, nil
 }
 
-func (s *assertingMultiService) PingError(ctx context.Context, ping *pb.PingRequest) (*pb.Empty, error) {
+func (s *assertingMultiService) PingError(ctx context.Context, ping *pb.PingRequest) (*pb.EmptyReply, error) {
 	return nil, status.Errorf(codes.FailedPrecondition, "Userspace error.")
 }
 
@@ -168,10 +168,14 @@ func (b *assertingBackend) AppendInfo(resp []byte) ([]byte, error) {
 }
 
 func (b *assertingBackend) BuildError(err error) ([]byte, error) {
-	return proto.Marshal(&pb.ResponseMetadataPrepender{
-		Metadata: &pb.ResponseMetadata{
-			Hostname:      fmt.Sprintf("server%d", b.i),
-			UpstreamError: err.Error(),
+	return proto.Marshal(&pb.EmptyReply{
+		Response: []*pb.EmptyResponse{
+			{
+				Metadata: &pb.ResponseMetadata{
+					Hostname:      fmt.Sprintf("server%d", b.i),
+					UpstreamError: err.Error(),
+				},
+			},
 		},
 	})
 }
@@ -216,6 +220,53 @@ func (s *MultiServiceSuite) TestPingEmptyCarriesClientMetadata() {
 	s.Require().Empty(expectedUpstreams)
 }
 
+func (s *MultiServiceSuite) TestPingEmpty_StressTest() {
+	for i := 0; i < 50; i++ {
+		s.TestPingEmptyCarriesClientMetadata()
+	}
+}
+
+func (s *MultiServiceSuite) TestPingCarriesServerHeadersAndTrailers() {
+	headerMd := make(metadata.MD)
+	trailerMd := make(metadata.MD)
+	// This is an awkward calling convention... but meh.
+	out, err := s.testClient.Ping(s.ctx, &pb.PingRequest{Value: "foo"}, grpc.Header(&headerMd), grpc.Trailer(&trailerMd))
+	require.NoError(s.T(), err, "Ping should succeed without errors")
+
+	s.Require().Len(out.Response, numUpstreams)
+	for _, resp := range out.Response {
+		s.Require().Equal("foo", resp.Value)
+		s.Require().EqualValues(42, resp.Counter)
+
+		// equal metadata set by proxy and server
+		s.Require().Equal(resp.Metadata.Hostname, resp.Server)
+	}
+
+	assert.Contains(s.T(), headerMd, serverHeaderMdKey, "server response headers must contain server data")
+	assert.Len(s.T(), trailerMd, 1, "server response trailers must contain server data")
+}
+
+func (s *MultiServiceSuite) TestPingErrorPropagatesAppError() {
+	out, err := s.testClient.PingError(s.ctx, &pb.PingRequest{Value: "foo"})
+	s.Require().NoError(err, "error should be encapsulated in the response")
+
+	s.Require().Len(out.Response, numUpstreams)
+	for _, resp := range out.Response {
+		s.Require().NotEmpty(resp.Metadata.UpstreamError)
+		s.Require().NotEmpty(resp.Metadata.Hostname)
+		s.Assert().Equal("rpc error: code = FailedPrecondition desc = Userspace error.", resp.Metadata.UpstreamError)
+	}
+}
+
+func (s *MultiServiceSuite) TestDirectorErrorIsPropagated() {
+	// See SetupSuite where the StreamDirector has a special case.
+	ctx := metadata.NewOutgoingContext(s.ctx, metadata.Pairs(rejectingMdKey, "true"))
+	_, err := s.testClient.Ping(ctx, &pb.PingRequest{Value: "foo"})
+	require.Error(s.T(), err, "Director should reject this RPC")
+	assert.Equal(s.T(), codes.PermissionDenied, status.Code(err))
+	assert.Equal(s.T(), "testing rejection", status.Convert(err).Message())
+}
+
 func (s *MultiServiceSuite) SetupTest() {
 	s.ctx, s.ctxCancel = context.WithTimeout(context.TODO(), 120*time.Second)
 }
diff --git a/testservice/test.pb.go b/testservice/test.pb.go
index 34ffba3..e270439 100644
--- a/testservice/test.pb.go
+++ b/testservice/test.pb.go
@@ -329,6 +329,84 @@ func (m *MultiPingReply) GetResponse() []*MultiPingResponse {
 	return nil
 }
 
+type EmptyReply struct {
+	Response             []*EmptyResponse `protobuf:"bytes,1,rep,name=response,proto3" json:"response,omitempty"`
+	XXX_NoUnkeyedLiteral struct{}         `json:"-"`
+	XXX_unrecognized     []byte           `json:"-"`
+	XXX_sizecache        int32            `json:"-"`
+}
+
+func (m *EmptyReply) Reset()         { *m = EmptyReply{} }
+func (m *EmptyReply) String() string { return proto.CompactTextString(m) }
+func (*EmptyReply) ProtoMessage()    {}
+func (*EmptyReply) Descriptor() ([]byte, []int) {
+	return fileDescriptor_c161fcfdc0c3ff1e, []int{7}
+}
+
+func (m *EmptyReply) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_EmptyReply.Unmarshal(m, b)
+}
+func (m *EmptyReply) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_EmptyReply.Marshal(b, m, deterministic)
+}
+func (m *EmptyReply) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_EmptyReply.Merge(m, src)
+}
+func (m *EmptyReply) XXX_Size() int {
+	return xxx_messageInfo_EmptyReply.Size(m)
+}
+func (m *EmptyReply) XXX_DiscardUnknown() {
+	xxx_messageInfo_EmptyReply.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_EmptyReply proto.InternalMessageInfo
+
+func (m *EmptyReply) GetResponse() []*EmptyResponse {
+	if m != nil {
+		return m.Response
+	}
+	return nil
+}
+
+type EmptyResponse struct {
+	Metadata             *ResponseMetadata `protobuf:"bytes,99,opt,name=metadata,proto3" json:"metadata,omitempty"`
+	XXX_NoUnkeyedLiteral struct{}          `json:"-"`
+	XXX_unrecognized     []byte            `json:"-"`
+	XXX_sizecache        int32             `json:"-"`
+}
+
+func (m *EmptyResponse) Reset()         { *m = EmptyResponse{} }
+func (m *EmptyResponse) String() string { return proto.CompactTextString(m) }
+func (*EmptyResponse) ProtoMessage()    {}
+func (*EmptyResponse) Descriptor() ([]byte, []int) {
+	return fileDescriptor_c161fcfdc0c3ff1e, []int{8}
+}
+
+func (m *EmptyResponse) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_EmptyResponse.Unmarshal(m, b)
+}
+func (m *EmptyResponse) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_EmptyResponse.Marshal(b, m, deterministic)
+}
+func (m *EmptyResponse) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_EmptyResponse.Merge(m, src)
+}
+func (m *EmptyResponse) XXX_Size() int {
+	return xxx_messageInfo_EmptyResponse.Size(m)
+}
+func (m *EmptyResponse) XXX_DiscardUnknown() {
+	xxx_messageInfo_EmptyResponse.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_EmptyResponse proto.InternalMessageInfo
+
+func (m *EmptyResponse) GetMetadata() *ResponseMetadata {
+	if m != nil {
+		return m.Metadata
+	}
+	return nil
+}
+
 func init() {
 	proto.RegisterType((*Empty)(nil), "smira.testproto.Empty")
 	proto.RegisterType((*PingRequest)(nil), "smira.testproto.PingRequest")
@@ -337,38 +415,43 @@ func init() {
 	proto.RegisterType((*ResponseMetadataPrepender)(nil), "smira.testproto.ResponseMetadataPrepender")
 	proto.RegisterType((*MultiPingResponse)(nil), "smira.testproto.MultiPingResponse")
 	proto.RegisterType((*MultiPingReply)(nil), "smira.testproto.MultiPingReply")
+	proto.RegisterType((*EmptyReply)(nil), "smira.testproto.EmptyReply")
+	proto.RegisterType((*EmptyResponse)(nil), "smira.testproto.EmptyResponse")
 }
 
 func init() { proto.RegisterFile("test.proto", fileDescriptor_c161fcfdc0c3ff1e) }
 
 var fileDescriptor_c161fcfdc0c3ff1e = []byte{
-	// 416 bytes of a gzipped FileDescriptorProto
-	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x09, 0x6e, 0x88, 0x02, 0xff, 0xac, 0x92, 0xcf, 0x4e, 0xea, 0x40,
-	0x14, 0xc6, 0x6f, 0xe1, 0x02, 0xe5, 0xc0, 0xe5, 0xde, 0x3b, 0x31, 0xa4, 0x12, 0x8d, 0x3a, 0xc6,
-	0x84, 0x55, 0x43, 0x70, 0x2d, 0x1b, 0x45, 0x17, 0x4a, 0xc4, 0xa2, 0x2e, 0xdc, 0x98, 0x0a, 0x13,
-	0x6d, 0x42, 0xff, 0x38, 0x33, 0x25, 0xe1, 0x05, 0x7c, 0x08, 0xdf, 0xd5, 0xc4, 0x99, 0xa1, 0x25,
-	0x48, 0x83, 0x2d, 0xc1, 0xe5, 0xf9, 0xe6, 0x3b, 0xbf, 0x39, 0x33, 0xdf, 0x01, 0xe0, 0x84, 0x71,
-	0x33, 0xa0, 0x3e, 0xf7, 0xd1, 0x5f, 0xe6, 0x3a, 0xd4, 0x36, 0xa5, 0xa2, 0x04, 0x5c, 0x82, 0x42,
-	0xd7, 0x0d, 0xf8, 0x14, 0x1f, 0x42, 0xa5, 0xef, 0x78, 0xcf, 0x16, 0x79, 0x0d, 0xc5, 0x21, 0xda,
-	0x82, 0xc2, 0xc4, 0x1e, 0x87, 0xc4, 0xd0, 0xf6, 0xb5, 0x66, 0xd9, 0x9a, 0x15, 0xb8, 0x03, 0xd5,
-	0x99, 0x89, 0x05, 0xbe, 0xc7, 0x88, 0x74, 0xdd, 0x2f, 0xba, 0x54, 0x81, 0x0c, 0x28, 0x0d, 0xfd,
-	0xd0, 0xe3, 0x84, 0x1a, 0x39, 0xa1, 0x17, 0xac, 0xb8, 0xc4, 0x77, 0xf0, 0x2f, 0xee, 0xed, 0x11,
-	0x6e, 0x8f, 0x6c, 0x6e, 0xa3, 0x06, 0xe8, 0x2f, 0x3e, 0xe3, 0x9e, 0xed, 0x12, 0x63, 0xa8, 0x30,
-	0xf3, 0x1a, 0x1d, 0x41, 0x2d, 0x0c, 0x18, 0xa7, 0xc4, 0x76, 0x1f, 0x09, 0xa5, 0x3e, 0x35, 0x46,
-	0xca, 0xf1, 0x27, 0x56, 0xbb, 0x52, 0xc4, 0x0f, 0xb0, 0xbd, 0x8c, 0xed, 0x53, 0x12, 0x10, 0x6f,
-	0x44, 0x28, 0x3a, 0x01, 0xdd, 0x8d, 0x44, 0xc5, 0xaf, 0xb4, 0x0f, 0xcc, 0xa5, 0x5f, 0x30, 0x97,
-	0xbb, 0xad, 0x79, 0x0b, 0x7e, 0xd7, 0xe0, 0x7f, 0x2f, 0x1c, 0x73, 0xe7, 0xcb, 0xc3, 0x37, 0x83,
-	0xae, 0xfb, 0x6f, 0xa8, 0x0e, 0x45, 0x46, 0xe8, 0x44, 0x1c, 0xe4, 0x55, 0x43, 0x54, 0xe1, 0x3e,
-	0xd4, 0x16, 0x66, 0x0b, 0xc6, 0x53, 0xd4, 0x01, 0x9d, 0x46, 0xf7, 0x0a, 0x78, 0x5e, 0x0c, 0x86,
-	0x13, 0x83, 0x25, 0x9e, 0x63, 0xcd, 0x7b, 0xda, 0x1f, 0x39, 0xa8, 0xdc, 0x0a, 0xe7, 0x40, 0x5c,
-	0xe0, 0x0c, 0x09, 0x3a, 0x83, 0xb2, 0x74, 0xaa, 0x1d, 0x41, 0xf5, 0x04, 0x4a, 0xe9, 0x8d, 0xdd,
-	0x84, 0xbe, 0x48, 0xc7, 0xbf, 0x50, 0x17, 0x7e, 0x4b, 0x05, 0xed, 0xac, 0x30, 0xaa, 0x9d, 0x4b,
-	0xc7, 0x9c, 0x46, 0xc3, 0xc8, 0xd0, 0x53, 0x58, 0x2b, 0x46, 0x15, 0x90, 0x4b, 0xd0, 0xa5, 0xf1,
-	0xca, 0x11, 0x5b, 0xbe, 0xd9, 0x3c, 0x2d, 0x0d, 0x5d, 0x03, 0x48, 0x6d, 0xa0, 0x96, 0x71, 0x43,
-	0x5c, 0x53, 0x6b, 0x69, 0xed, 0xb7, 0x3c, 0x54, 0x55, 0x3e, 0x71, 0x00, 0xe7, 0x59, 0x02, 0xd8,
-	0xfb, 0x2e, 0x63, 0xb1, 0x16, 0xe2, 0xd9, 0x17, 0x99, 0x22, 0xc8, 0x00, 0xfa, 0x91, 0x10, 0x7a,
-	0x99, 0x43, 0x48, 0x9f, 0x48, 0xc4, 0x70, 0xb3, 0x46, 0x0c, 0xe9, 0x40, 0x19, 0xc4, 0x53, 0x51,
-	0x9d, 0x1d, 0x7f, 0x06, 0x00, 0x00, 0xff, 0xff, 0x6a, 0xdd, 0xde, 0x4d, 0x3e, 0x05, 0x00, 0x00,
+	// 450 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x09, 0x6e, 0x88, 0x02, 0xff, 0xa4, 0x93, 0xcd, 0x6e, 0xda, 0x40,
+	0x10, 0xc7, 0x6b, 0x28, 0x60, 0x86, 0x8f, 0xb6, 0xab, 0x0a, 0xb9, 0xf4, 0x7b, 0xab, 0x4a, 0x9c,
+	0x2c, 0x44, 0x6f, 0x95, 0xca, 0xa5, 0xa5, 0x41, 0x4a, 0x48, 0x88, 0x49, 0x72, 0xc8, 0x25, 0x72,
+	0x60, 0x95, 0x58, 0xc2, 0x1f, 0x59, 0xaf, 0x91, 0x78, 0x86, 0xbc, 0x41, 0xde, 0x35, 0x52, 0x76,
+	0xd7, 0x36, 0x02, 0x1c, 0x62, 0x23, 0x1f, 0xe7, 0xbf, 0x33, 0xbf, 0x9d, 0xd9, 0xff, 0x2c, 0x00,
+	0x23, 0x3e, 0xd3, 0x3d, 0xea, 0x32, 0x17, 0xbd, 0xf1, 0x6d, 0x8b, 0x9a, 0xba, 0x50, 0xa4, 0x80,
+	0x2b, 0x50, 0x1a, 0xd8, 0x1e, 0x5b, 0xe2, 0x1f, 0x50, 0x1b, 0x5b, 0xce, 0x8d, 0x41, 0xee, 0x02,
+	0x7e, 0x88, 0xde, 0x43, 0x69, 0x61, 0xce, 0x03, 0xa2, 0x29, 0xdf, 0x94, 0x4e, 0xd5, 0x08, 0x03,
+	0xdc, 0x87, 0x7a, 0x98, 0xe4, 0x7b, 0xae, 0xe3, 0x13, 0x91, 0x75, 0xb1, 0x9e, 0x25, 0x03, 0xa4,
+	0x41, 0x65, 0xea, 0x06, 0x0e, 0x23, 0x54, 0x2b, 0x70, 0xbd, 0x64, 0xc4, 0x21, 0x3e, 0x87, 0xb7,
+	0x71, 0xed, 0x88, 0x30, 0x73, 0x66, 0x32, 0x13, 0xb5, 0x41, 0xbd, 0x75, 0x7d, 0xe6, 0x98, 0x36,
+	0xd1, 0xa6, 0x12, 0xb3, 0x8a, 0xd1, 0x4f, 0x68, 0x06, 0x9e, 0xcf, 0x28, 0x31, 0xed, 0x2b, 0x42,
+	0xa9, 0x4b, 0xb5, 0x99, 0xcc, 0x68, 0xc4, 0xea, 0x40, 0x88, 0xf8, 0x12, 0x3e, 0x6c, 0x63, 0xc7,
+	0x94, 0x78, 0xc4, 0x99, 0x11, 0x8a, 0xfe, 0x80, 0x6a, 0x47, 0xa2, 0xe4, 0xd7, 0x7a, 0xdf, 0xf5,
+	0xad, 0x57, 0xd0, 0xb7, 0xab, 0x8d, 0x55, 0x09, 0x7e, 0x50, 0xe0, 0xdd, 0x28, 0x98, 0x33, 0x6b,
+	0x63, 0xf0, 0x7c, 0xd0, 0x7d, 0xdf, 0x0d, 0xb5, 0xa0, 0xec, 0x13, 0xba, 0xe0, 0x07, 0x45, 0x59,
+	0x10, 0x45, 0x78, 0x0c, 0xcd, 0xb5, 0xde, 0xbc, 0xf9, 0x12, 0xf5, 0x41, 0xa5, 0xd1, 0xbd, 0x1c,
+	0x5e, 0xe4, 0x8d, 0xe1, 0x44, 0x63, 0x89, 0x71, 0x8c, 0x55, 0x0d, 0x1e, 0x02, 0xc8, 0x7d, 0x08,
+	0x69, 0xbf, 0x13, 0xb4, 0x2f, 0x09, 0x5a, 0x94, 0x9e, 0x20, 0x1d, 0x43, 0x63, 0xe3, 0x28, 0xe7,
+	0x9b, 0xf5, 0x1e, 0x0b, 0x50, 0x3b, 0xe3, 0x89, 0x13, 0x3e, 0xba, 0x35, 0x25, 0xe8, 0x1f, 0x54,
+	0xc5, 0x0c, 0xf2, 0x0e, 0xd4, 0x7a, 0xbe, 0xad, 0xf6, 0xe7, 0x84, 0xbe, 0x3e, 0x37, 0x7e, 0x85,
+	0x06, 0xf0, 0x5a, 0x28, 0xe8, 0xd3, 0x8e, 0x44, 0xf9, 0x1b, 0xd2, 0x31, 0x7f, 0xa3, 0x66, 0xc4,
+	0x3a, 0xa6, 0xb0, 0x76, 0xb4, 0xca, 0x21, 0x87, 0xa0, 0x8a, 0xc4, 0x23, 0x8b, 0xff, 0xbf, 0x7c,
+	0xfd, 0x74, 0x15, 0x74, 0x02, 0x20, 0xb4, 0x89, 0xfc, 0x26, 0x39, 0x71, 0x1d, 0xa5, 0xab, 0xf4,
+	0xee, 0x8b, 0x50, 0x97, 0x9b, 0x13, 0x1b, 0xf0, 0x3f, 0x8b, 0x01, 0x5f, 0x5f, 0xda, 0x3e, 0xbe,
+	0x62, 0x7c, 0xec, 0x83, 0x4c, 0x16, 0x64, 0x00, 0x0d, 0xb3, 0x9b, 0xf0, 0x71, 0xd7, 0x1a, 0x87,
+	0xa4, 0x51, 0x66, 0x27, 0xd2, 0xdb, 0xe2, 0x5e, 0x9c, 0xee, 0xe1, 0x45, 0x3a, 0x50, 0xb8, 0x71,
+	0x5d, 0x96, 0x67, 0xbf, 0x9e, 0x02, 0x00, 0x00, 0xff, 0xff, 0xbf, 0x8b, 0x3b, 0x5d, 0xdd, 0x05,
+	0x00, 0x00,
 }
 
 // Reference imports to suppress errors if they are not otherwise used.
@@ -661,7 +744,7 @@ var _TestService_serviceDesc = grpc.ServiceDesc{
 type MultiServiceClient interface {
 	PingEmpty(ctx context.Context, in *Empty, opts ...grpc.CallOption) (*MultiPingReply, error)
 	Ping(ctx context.Context, in *PingRequest, opts ...grpc.CallOption) (*MultiPingReply, error)
-	PingError(ctx context.Context, in *PingRequest, opts ...grpc.CallOption) (*Empty, error)
+	PingError(ctx context.Context, in *PingRequest, opts ...grpc.CallOption) (*EmptyReply, error)
 	PingList(ctx context.Context, in *PingRequest, opts ...grpc.CallOption) (MultiService_PingListClient, error)
 	PingStream(ctx context.Context, opts ...grpc.CallOption) (MultiService_PingStreamClient, error)
 }
@@ -692,8 +775,8 @@ func (c *multiServiceClient) Ping(ctx context.Context, in *PingRequest, opts ...
 	return out, nil
 }
 
-func (c *multiServiceClient) PingError(ctx context.Context, in *PingRequest, opts ...grpc.CallOption) (*Empty, error) {
-	out := new(Empty)
+func (c *multiServiceClient) PingError(ctx context.Context, in *PingRequest, opts ...grpc.CallOption) (*EmptyReply, error) {
+	out := new(EmptyReply)
 	err := c.cc.Invoke(ctx, "/smira.testproto.MultiService/PingError", in, out, opts...)
 	if err != nil {
 		return nil, err
@@ -768,7 +851,7 @@ func (x *multiServicePingStreamClient) Recv() (*MultiPingReply, error) {
 type MultiServiceServer interface {
 	PingEmpty(context.Context, *Empty) (*MultiPingReply, error)
 	Ping(context.Context, *PingRequest) (*MultiPingReply, error)
-	PingError(context.Context, *PingRequest) (*Empty, error)
+	PingError(context.Context, *PingRequest) (*EmptyReply, error)
 	PingList(*PingRequest, MultiService_PingListServer) error
 	PingStream(MultiService_PingStreamServer) error
 }
@@ -783,7 +866,7 @@ func (*UnimplementedMultiServiceServer) PingEmpty(ctx context.Context, req *Empt
 func (*UnimplementedMultiServiceServer) Ping(ctx context.Context, req *PingRequest) (*MultiPingReply, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method Ping not implemented")
 }
-func (*UnimplementedMultiServiceServer) PingError(ctx context.Context, req *PingRequest) (*Empty, error) {
+func (*UnimplementedMultiServiceServer) PingError(ctx context.Context, req *PingRequest) (*EmptyReply, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method PingError not implemented")
 }
 func (*UnimplementedMultiServiceServer) PingList(req *PingRequest, srv MultiService_PingListServer) error {
diff --git a/testservice/test.proto b/testservice/test.proto
index 89bf33c..633ebce 100644
--- a/testservice/test.proto
+++ b/testservice/test.proto
@@ -47,12 +47,20 @@ message MultiPingReply {
   repeated MultiPingResponse response = 1;
 }
 
+message EmptyReply {
+  repeated EmptyResponse response = 1;
+}
+
+message EmptyResponse {
+  ResponseMetadata metadata = 99;
+}
+
 service MultiService {
   rpc PingEmpty(Empty) returns (MultiPingReply) {}
 
   rpc Ping(PingRequest) returns (MultiPingReply) {}
 
-  rpc PingError(PingRequest) returns (Empty) {}
+  rpc PingError(PingRequest) returns (EmptyReply) {}
 
   rpc PingList(PingRequest) returns (stream MultiPingReply) {}