diff --git a/_examples/04_timeout/grpc/federation/federation.pb.go b/_examples/04_timeout/grpc/federation/federation.pb.go
index 39b3442a..285731ed 100644
--- a/_examples/04_timeout/grpc/federation/federation.pb.go
+++ b/_examples/04_timeout/grpc/federation/federation.pb.go
@@ -7,6 +7,7 @@
 package federation
 
 import (
+	_ "github.com/mercari/grpc-federation/grpc/federation/cel"
 	code "google.golang.org/genproto/googleapis/rpc/code"
 	errdetails "google.golang.org/genproto/googleapis/rpc/errdetails"
 	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
@@ -4075,7 +4076,6 @@ func file_grpc_federation_federation_proto_init() {
 	if File_grpc_federation_federation_proto != nil {
 		return
 	}
-	file_grpc_federation_private_proto_init()
 	if !protoimpl.UnsafeEnabled {
 		file_grpc_federation_federation_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*EnumRule); i {
diff --git a/_examples/05_async/grpc/federation/federation.pb.go b/_examples/05_async/grpc/federation/federation.pb.go
index 39b3442a..285731ed 100644
--- a/_examples/05_async/grpc/federation/federation.pb.go
+++ b/_examples/05_async/grpc/federation/federation.pb.go
@@ -7,6 +7,7 @@
 package federation
 
 import (
+	_ "github.com/mercari/grpc-federation/grpc/federation/cel"
 	code "google.golang.org/genproto/googleapis/rpc/code"
 	errdetails "google.golang.org/genproto/googleapis/rpc/errdetails"
 	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
@@ -4075,7 +4076,6 @@ func file_grpc_federation_federation_proto_init() {
 	if File_grpc_federation_federation_proto != nil {
 		return
 	}
-	file_grpc_federation_private_proto_init()
 	if !protoimpl.UnsafeEnabled {
 		file_grpc_federation_federation_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*EnumRule); i {
diff --git a/_examples/06_alias/grpc/federation/federation.pb.go b/_examples/06_alias/grpc/federation/federation.pb.go
index 39b3442a..285731ed 100644
--- a/_examples/06_alias/grpc/federation/federation.pb.go
+++ b/_examples/06_alias/grpc/federation/federation.pb.go
@@ -7,6 +7,7 @@
 package federation
 
 import (
+	_ "github.com/mercari/grpc-federation/grpc/federation/cel"
 	code "google.golang.org/genproto/googleapis/rpc/code"
 	errdetails "google.golang.org/genproto/googleapis/rpc/errdetails"
 	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
@@ -4075,7 +4076,6 @@ func file_grpc_federation_federation_proto_init() {
 	if File_grpc_federation_federation_proto != nil {
 		return
 	}
-	file_grpc_federation_private_proto_init()
 	if !protoimpl.UnsafeEnabled {
 		file_grpc_federation_federation_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*EnumRule); i {
diff --git a/_examples/09_multi_user/grpc/federation/federation.pb.go b/_examples/09_multi_user/grpc/federation/federation.pb.go
index 39b3442a..285731ed 100644
--- a/_examples/09_multi_user/grpc/federation/federation.pb.go
+++ b/_examples/09_multi_user/grpc/federation/federation.pb.go
@@ -7,6 +7,7 @@
 package federation
 
 import (
+	_ "github.com/mercari/grpc-federation/grpc/federation/cel"
 	code "google.golang.org/genproto/googleapis/rpc/code"
 	errdetails "google.golang.org/genproto/googleapis/rpc/errdetails"
 	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
@@ -4075,7 +4076,6 @@ func file_grpc_federation_federation_proto_init() {
 	if File_grpc_federation_federation_proto != nil {
 		return
 	}
-	file_grpc_federation_private_proto_init()
 	if !protoimpl.UnsafeEnabled {
 		file_grpc_federation_federation_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*EnumRule); i {
diff --git a/_examples/10_oneof/grpc/federation/federation.pb.go b/_examples/10_oneof/grpc/federation/federation.pb.go
index 39b3442a..285731ed 100644
--- a/_examples/10_oneof/grpc/federation/federation.pb.go
+++ b/_examples/10_oneof/grpc/federation/federation.pb.go
@@ -7,6 +7,7 @@
 package federation
 
 import (
+	_ "github.com/mercari/grpc-federation/grpc/federation/cel"
 	code "google.golang.org/genproto/googleapis/rpc/code"
 	errdetails "google.golang.org/genproto/googleapis/rpc/errdetails"
 	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
@@ -4075,7 +4076,6 @@ func file_grpc_federation_federation_proto_init() {
 	if File_grpc_federation_federation_proto != nil {
 		return
 	}
-	file_grpc_federation_private_proto_init()
 	if !protoimpl.UnsafeEnabled {
 		file_grpc_federation_federation_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*EnumRule); i {
diff --git a/_examples/11_multi_service/grpc/federation/federation.pb.go b/_examples/11_multi_service/grpc/federation/federation.pb.go
index 39b3442a..285731ed 100644
--- a/_examples/11_multi_service/grpc/federation/federation.pb.go
+++ b/_examples/11_multi_service/grpc/federation/federation.pb.go
@@ -7,6 +7,7 @@
 package federation
 
 import (
+	_ "github.com/mercari/grpc-federation/grpc/federation/cel"
 	code "google.golang.org/genproto/googleapis/rpc/code"
 	errdetails "google.golang.org/genproto/googleapis/rpc/errdetails"
 	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
@@ -4075,7 +4076,6 @@ func file_grpc_federation_federation_proto_init() {
 	if File_grpc_federation_federation_proto != nil {
 		return
 	}
-	file_grpc_federation_private_proto_init()
 	if !protoimpl.UnsafeEnabled {
 		file_grpc_federation_federation_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*EnumRule); i {
diff --git a/_examples/14_condition/grpc/federation/federation.pb.go b/_examples/14_condition/grpc/federation/federation.pb.go
index 39b3442a..285731ed 100644
--- a/_examples/14_condition/grpc/federation/federation.pb.go
+++ b/_examples/14_condition/grpc/federation/federation.pb.go
@@ -7,6 +7,7 @@
 package federation
 
 import (
+	_ "github.com/mercari/grpc-federation/grpc/federation/cel"
 	code "google.golang.org/genproto/googleapis/rpc/code"
 	errdetails "google.golang.org/genproto/googleapis/rpc/errdetails"
 	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
@@ -4075,7 +4076,6 @@ func file_grpc_federation_federation_proto_init() {
 	if File_grpc_federation_federation_proto != nil {
 		return
 	}
-	file_grpc_federation_private_proto_init()
 	if !protoimpl.UnsafeEnabled {
 		file_grpc_federation_federation_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*EnumRule); i {
diff --git a/_examples/17_error_handler/federation/federation.pb.go b/_examples/17_error_handler/federation/federation.pb.go
index 5f206ff4..5216e5a5 100644
--- a/_examples/17_error_handler/federation/federation.pb.go
+++ b/_examples/17_error_handler/federation/federation.pb.go
@@ -282,14 +282,14 @@ var file_federation_federation_proto_rawDesc = []byte{
 	0x74, 0x69, 0x6f, 0x6e, 0x2e, 0x50, 0x6f, 0x73, 0x74, 0x42, 0x09, 0x9a, 0x4a, 0x06, 0x12, 0x04,
 	0x70, 0x6f, 0x73, 0x74, 0x52, 0x04, 0x70, 0x6f, 0x73, 0x74, 0x3a, 0x1f, 0x9a, 0x4a, 0x1c, 0x0a,
 	0x1a, 0x0a, 0x04, 0x70, 0x6f, 0x73, 0x74, 0x6a, 0x12, 0x0a, 0x04, 0x50, 0x6f, 0x73, 0x74, 0x12,
-	0x0a, 0x0a, 0x02, 0x69, 0x64, 0x12, 0x04, 0x24, 0x2e, 0x69, 0x64, 0x22, 0xed, 0x03, 0x0a, 0x04,
+	0x0a, 0x0a, 0x02, 0x69, 0x64, 0x12, 0x04, 0x24, 0x2e, 0x69, 0x64, 0x22, 0xf7, 0x03, 0x0a, 0x04,
 	0x50, 0x6f, 0x73, 0x74, 0x12, 0x0e, 0x0a, 0x02, 0x69, 0x64, 0x18, 0x01, 0x20, 0x01, 0x28, 0x09,
 	0x52, 0x02, 0x69, 0x64, 0x12, 0x14, 0x0a, 0x05, 0x74, 0x69, 0x74, 0x6c, 0x65, 0x18, 0x02, 0x20,
-	0x01, 0x28, 0x09, 0x52, 0x05, 0x74, 0x69, 0x74, 0x6c, 0x65, 0x3a, 0xbe, 0x03, 0x9a, 0x4a, 0xba,
-	0x03, 0x0a, 0xa3, 0x03, 0x0a, 0x03, 0x72, 0x65, 0x73, 0x72, 0x9b, 0x03, 0x0a, 0x18, 0x70, 0x6f,
+	0x01, 0x28, 0x09, 0x52, 0x05, 0x74, 0x69, 0x74, 0x6c, 0x65, 0x3a, 0xc8, 0x03, 0x9a, 0x4a, 0xc4,
+	0x03, 0x0a, 0xad, 0x03, 0x0a, 0x03, 0x72, 0x65, 0x73, 0x72, 0xa5, 0x03, 0x0a, 0x18, 0x70, 0x6f,
 	0x73, 0x74, 0x2e, 0x50, 0x6f, 0x73, 0x74, 0x53, 0x65, 0x72, 0x76, 0x69, 0x63, 0x65, 0x2f, 0x47,
 	0x65, 0x74, 0x50, 0x6f, 0x73, 0x74, 0x12, 0x0a, 0x0a, 0x02, 0x69, 0x64, 0x12, 0x04, 0x24, 0x2e,
-	0x69, 0x64, 0x2a, 0xea, 0x02, 0x0a, 0x0a, 0x0a, 0x02, 0x69, 0x64, 0x5a, 0x04, 0x24, 0x2e, 0x69,
+	0x69, 0x64, 0x2a, 0xf4, 0x02, 0x0a, 0x0a, 0x0a, 0x02, 0x69, 0x64, 0x5a, 0x04, 0x24, 0x2e, 0x69,
 	0x64, 0x12, 0x95, 0x01, 0x65, 0x72, 0x72, 0x6f, 0x72, 0x2e, 0x70, 0x72, 0x65, 0x63, 0x6f, 0x6e,
 	0x64, 0x69, 0x74, 0x69, 0x6f, 0x6e, 0x5f, 0x66, 0x61, 0x69, 0x6c, 0x75, 0x72, 0x65, 0x73, 0x5b,
 	0x30, 0x5d, 0x2e, 0x76, 0x69, 0x6f, 0x6c, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x73, 0x5b, 0x30, 0x5d,
@@ -301,47 +301,48 @@ var file_federation_federation_proto_rawDesc = []byte{
 	0x74, 0x6f, 0x6d, 0x5f, 0x6d, 0x65, 0x73, 0x73, 0x61, 0x67, 0x65, 0x73, 0x5b, 0x30, 0x5d, 0x2e,
 	0x69, 0x64, 0x20, 0x3d, 0x3d, 0x20, 0x27, 0x78, 0x27, 0x18, 0x09, 0x22, 0x1e, 0x27, 0x74, 0x68,
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+	0x27, 0x20, 0x2b, 0x20, 0x24, 0x2e, 0x76, 0x61, 0x6c, 0x75, 0x65, 0x52, 0x05, 0x76, 0x61, 0x6c,
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+	0x42, 0x33, 0x9a, 0x4a, 0x30, 0x12, 0x2e, 0x27, 0x63, 0x75, 0x73, 0x74, 0x6f, 0x6d, 0x20, 0x65,
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+	0x20, 0x24, 0x2e, 0x65, 0x72, 0x72, 0x6f, 0x72, 0x5f, 0x69, 0x6e, 0x66, 0x6f, 0x2e, 0x6d, 0x65,
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+	0x4c, 0x0a, 0x07, 0x47, 0x65, 0x74, 0x50, 0x6f, 0x73, 0x74, 0x12, 0x1e, 0x2e, 0x6f, 0x72, 0x67,
+	0x2e, 0x66, 0x65, 0x64, 0x65, 0x72, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x2e, 0x47, 0x65, 0x74, 0x50,
+	0x6f, 0x73, 0x74, 0x52, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x1a, 0x1f, 0x2e, 0x6f, 0x72, 0x67,
+	0x2e, 0x66, 0x65, 0x64, 0x65, 0x72, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x2e, 0x47, 0x65, 0x74, 0x50,
+	0x6f, 0x73, 0x74, 0x52, 0x65, 0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65, 0x22, 0x00, 0x1a, 0x17, 0x9a,
+	0x4a, 0x14, 0x0a, 0x12, 0x12, 0x10, 0x70, 0x6f, 0x73, 0x74, 0x2e, 0x50, 0x6f, 0x73, 0x74, 0x53,
+	0x65, 0x72, 0x76, 0x69, 0x63, 0x65, 0x42, 0x9d, 0x01, 0x0a, 0x12, 0x63, 0x6f, 0x6d, 0x2e, 0x6f,
+	0x72, 0x67, 0x2e, 0x66, 0x65, 0x64, 0x65, 0x72, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x42, 0x0f, 0x46,
+	0x65, 0x64, 0x65, 0x72, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x50, 0x72, 0x6f, 0x74, 0x6f, 0x50, 0x01,
+	0x5a, 0x1d, 0x65, 0x78, 0x61, 0x6d, 0x70, 0x6c, 0x65, 0x2f, 0x66, 0x65, 0x64, 0x65, 0x72, 0x61,
+	0x74, 0x69, 0x6f, 0x6e, 0x3b, 0x66, 0x65, 0x64, 0x65, 0x72, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0xa2,
+	0x02, 0x03, 0x4f, 0x46, 0x58, 0xaa, 0x02, 0x0e, 0x4f, 0x72, 0x67, 0x2e, 0x46, 0x65, 0x64, 0x65,
+	0x72, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0xca, 0x02, 0x0e, 0x4f, 0x72, 0x67, 0x5c, 0x46, 0x65, 0x64,
+	0x65, 0x72, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0xe2, 0x02, 0x1a, 0x4f, 0x72, 0x67, 0x5c, 0x46, 0x65,
+	0x64, 0x65, 0x72, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x5c, 0x47, 0x50, 0x42, 0x4d, 0x65, 0x74, 0x61,
+	0x64, 0x61, 0x74, 0x61, 0xea, 0x02, 0x0f, 0x4f, 0x72, 0x67, 0x3a, 0x3a, 0x46, 0x65, 0x64, 0x65,
+	0x72, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
diff --git a/_examples/17_error_handler/federation/federation_grpc_federation.pb.go b/_examples/17_error_handler/federation/federation_grpc_federation.pb.go
index 9f1ac4c1..e52f9944 100644
--- a/_examples/17_error_handler/federation/federation_grpc_federation.pb.go
+++ b/_examples/17_error_handler/federation/federation_grpc_federation.pb.go
@@ -22,8 +22,8 @@ var (
 
 // Org_Federation_CustomMessageArgument is argument for "org.federation.CustomMessage" message.
 type Org_Federation_CustomMessageArgument[T any] struct {
-	Msg    string
-	Client T
+	ErrorInfo *grpcfedcel.Error
+	Client    T
 }
 
 // Org_Federation_GetPostResponseArgument is argument for "org.federation.GetPostResponse" message.
@@ -137,7 +137,7 @@ func NewFederationService(cfg FederationServiceConfig) (*FederationService, erro
 	}
 	celHelper := grpcfed.NewCELTypeHelper(map[string]map[string]*grpcfed.CELFieldType{
 		"grpc.federation.private.CustomMessageArgument": {
-			"msg": grpcfed.NewCELFieldType(grpcfed.CELStringType, "Msg"),
+			"error_info": grpcfed.NewCELFieldType(grpcfed.NewCELObjectType("grpc.federation.private.Error"), "ErrorInfo"),
 		},
 		"grpc.federation.private.GetPostResponseArgument": {
 			"id": grpcfed.NewCELFieldType(grpcfed.CELStringType, "Id"),
@@ -207,8 +207,8 @@ func (s *FederationService) resolve_Org_Federation_CustomMessage(ctx context.Con
 	ret := &CustomMessage{}
 
 	// field binding section.
-	// (grpc.federation.field).by = "'custom error message:' + $.msg"
-	if err := grpcfed.SetCELValue(ctx, value, "'custom error message:' + $.msg", func(v string) { ret.Msg = v }); err != nil {
+	// (grpc.federation.field).by = "'custom error message:' + $.error_info.message"
+	if err := grpcfed.SetCELValue(ctx, value, "'custom error message:' + $.error_info.message", func(v string) { ret.Msg = v }); err != nil {
 		grpcfed.RecordErrorToSpan(ctx, err)
 		return nil, err
 	}
@@ -421,7 +421,7 @@ func (s *FederationService) resolve_Org_Federation_Post(ctx context.Context, req
 						     name: "_def0_err_detail0_msg0"
 						     message {
 						       name: "CustomMessage"
-						       args { name: "msg", by: "id" }
+						       args { name: "error_info", by: "error" }
 						     }
 						   }
 						*/
@@ -433,9 +433,9 @@ func (s *FederationService) resolve_Org_Federation_Post(ctx context.Context, req
 								args := &Org_Federation_CustomMessageArgument[*FederationServiceDependentClientSet]{
 									Client: s.client,
 								}
-								// { name: "msg", by: "id" }
-								if err := grpcfed.SetCELValue(ctx, value, "id", func(v string) {
-									args.Msg = v
+								// { name: "error_info", by: "error" }
+								if err := grpcfed.SetCELValue(ctx, value, "error", func(v *grpcfedcel.Error) {
+									args.ErrorInfo = v
 								}); err != nil {
 									return nil, err
 								}
@@ -564,6 +564,13 @@ func (s *FederationService) resolve_Org_Federation_Post(ctx context.Context, req
 	return ret, nil
 }
 
+func (s *FederationService) logvalue_Grpc_Federation_Private_Error(v *grpcfedcel.Error) slog.Value {
+	if v == nil {
+		return slog.GroupValue()
+	}
+	return slog.GroupValue()
+}
+
 func (s *FederationService) logvalue_Org_Federation_CustomMessage(v *CustomMessage) slog.Value {
 	if v == nil {
 		return slog.GroupValue()
@@ -578,7 +585,7 @@ func (s *FederationService) logvalue_Org_Federation_CustomMessageArgument(v *Org
 		return slog.GroupValue()
 	}
 	return slog.GroupValue(
-		slog.String("msg", v.Msg),
+		slog.Any("error_info", s.logvalue_Grpc_Federation_Private_Error(v.ErrorInfo)),
 	)
 }
 
diff --git a/_examples/17_error_handler/grpc/federation/federation.pb.go b/_examples/17_error_handler/grpc/federation/federation.pb.go
index 39b3442a..285731ed 100644
--- a/_examples/17_error_handler/grpc/federation/federation.pb.go
+++ b/_examples/17_error_handler/grpc/federation/federation.pb.go
@@ -7,6 +7,7 @@
 package federation
 
 import (
+	_ "github.com/mercari/grpc-federation/grpc/federation/cel"
 	code "google.golang.org/genproto/googleapis/rpc/code"
 	errdetails "google.golang.org/genproto/googleapis/rpc/errdetails"
 	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
@@ -4075,7 +4076,6 @@ func file_grpc_federation_federation_proto_init() {
 	if File_grpc_federation_federation_proto != nil {
 		return
 	}
-	file_grpc_federation_private_proto_init()
 	if !protoimpl.UnsafeEnabled {
 		file_grpc_federation_federation_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*EnumRule); i {
diff --git a/_examples/17_error_handler/proto/federation/federation.proto b/_examples/17_error_handler/proto/federation/federation.proto
index 5f2f4b0e..10d464c6 100644
--- a/_examples/17_error_handler/proto/federation/federation.proto
+++ b/_examples/17_error_handler/proto/federation/federation.proto
@@ -48,7 +48,7 @@ message Post {
             message: "'this is custom error message'"
             details {
               def { name: "localized_msg" message { name: "LocalizedMessage" args { name: "value" by: "id" } } }
-              message { name: "CustomMessage" args { name: "msg" by: "id" } }
+              message { name: "CustomMessage" args { name: "error_info" by: "error" } }
               precondition_failure {
                 violations {
                   type: "'some-type'"
@@ -82,5 +82,5 @@ message LocalizedMessage {
 }
 
 message CustomMessage {
-  string msg = 1 [(grpc.federation.field).by = "'custom error message:' + $.msg"];
+  string msg = 1 [(grpc.federation.field).by = "'custom error message:' + $.error_info.message"];
 }
\ No newline at end of file
diff --git a/grpc/federation/cel.go b/grpc/federation/cel.go
index d6bb953e..40f575ce 100644
--- a/grpc/federation/cel.go
+++ b/grpc/federation/cel.go
@@ -559,7 +559,7 @@ func SetGRPCError(ctx context.Context, value localValue, err error) {
 	if !ok {
 		return
 	}
-	grpcErr := &Error{
+	grpcErr := &grpcfedcel.Error{
 		Code:    int32(stat.Code()),
 		Message: stat.Message(),
 	}
diff --git a/grpc/federation/private.pb.go b/grpc/federation/cel/private.pb.go
similarity index 98%
rename from grpc/federation/private.pb.go
rename to grpc/federation/cel/private.pb.go
index d9504aba..ae73488f 100644
--- a/grpc/federation/private.pb.go
+++ b/grpc/federation/cel/private.pb.go
@@ -4,7 +4,7 @@
 // 	protoc        (unknown)
 // source: grpc/federation/private.proto
 
-package federation
+package cel
 
 import (
 	errdetails "google.golang.org/genproto/googleapis/rpc/errdetails"
@@ -232,12 +232,12 @@ var file_grpc_federation_private_proto_rawDesc = []byte{
 	0x65, 0x73, 0x73, 0x61, 0x67, 0x65, 0x73, 0x18, 0x0e, 0x20, 0x03, 0x28, 0x0b, 0x32, 0x1c, 0x2e,
 	0x67, 0x6f, 0x6f, 0x67, 0x6c, 0x65, 0x2e, 0x72, 0x70, 0x63, 0x2e, 0x4c, 0x6f, 0x63, 0x61, 0x6c,
 	0x69, 0x7a, 0x65, 0x64, 0x4d, 0x65, 0x73, 0x73, 0x61, 0x67, 0x65, 0x52, 0x11, 0x6c, 0x6f, 0x63,
-	0x61, 0x6c, 0x69, 0x7a, 0x65, 0x64, 0x4d, 0x65, 0x73, 0x73, 0x61, 0x67, 0x65, 0x73, 0x42, 0x3f,
-	0x5a, 0x3d, 0x67, 0x69, 0x74, 0x68, 0x75, 0x62, 0x2e, 0x63, 0x6f, 0x6d, 0x2f, 0x6d, 0x65, 0x72,
+	0x61, 0x6c, 0x69, 0x7a, 0x65, 0x64, 0x4d, 0x65, 0x73, 0x73, 0x61, 0x67, 0x65, 0x73, 0x42, 0x3c,
+	0x5a, 0x3a, 0x67, 0x69, 0x74, 0x68, 0x75, 0x62, 0x2e, 0x63, 0x6f, 0x6d, 0x2f, 0x6d, 0x65, 0x72,
 	0x63, 0x61, 0x72, 0x69, 0x2f, 0x67, 0x72, 0x70, 0x63, 0x2d, 0x66, 0x65, 0x64, 0x65, 0x72, 0x61,
 	0x74, 0x69, 0x6f, 0x6e, 0x2f, 0x67, 0x72, 0x70, 0x63, 0x2f, 0x66, 0x65, 0x64, 0x65, 0x72, 0x61,
-	0x74, 0x69, 0x6f, 0x6e, 0x3b, 0x66, 0x65, 0x64, 0x65, 0x72, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x62,
-	0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
+	0x74, 0x69, 0x6f, 0x6e, 0x2f, 0x63, 0x65, 0x6c, 0x3b, 0x63, 0x65, 0x6c, 0x62, 0x06, 0x70, 0x72,
+	0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
diff --git a/grpc/federation/private_vtproto.pb.go b/grpc/federation/cel/private_vtproto.pb.go
similarity index 99%
rename from grpc/federation/private_vtproto.pb.go
rename to grpc/federation/cel/private_vtproto.pb.go
index e65092c6..68856fbc 100644
--- a/grpc/federation/private_vtproto.pb.go
+++ b/grpc/federation/cel/private_vtproto.pb.go
@@ -2,7 +2,7 @@
 // protoc-gen-go-vtproto version: v0.6.0
 // source: grpc/federation/private.proto
 
-package federation
+package cel
 
 import (
 	fmt "fmt"
diff --git a/grpc/federation/federation.pb.go b/grpc/federation/federation.pb.go
index 7e20655e..d9bd9c21 100644
--- a/grpc/federation/federation.pb.go
+++ b/grpc/federation/federation.pb.go
@@ -7,6 +7,7 @@
 package federation
 
 import (
+	_ "github.com/mercari/grpc-federation/grpc/federation/cel"
 	code "google.golang.org/genproto/googleapis/rpc/code"
 	errdetails "google.golang.org/genproto/googleapis/rpc/errdetails"
 	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
@@ -4067,7 +4068,6 @@ func file_grpc_federation_federation_proto_init() {
 	if File_grpc_federation_federation_proto != nil {
 		return
 	}
-	file_grpc_federation_private_proto_init()
 	if !protoimpl.UnsafeEnabled {
 		file_grpc_federation_federation_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*EnumRule); i {
diff --git a/proto/grpc/federation/private.proto b/proto/grpc/federation/private.proto
index cbcc7daf..e2a5aa1d 100644
--- a/proto/grpc/federation/private.proto
+++ b/proto/grpc/federation/private.proto
@@ -5,7 +5,7 @@ package grpc.federation.private;
 import "google/protobuf/any.proto";
 import "google/rpc/error_details.proto";
 
-option go_package = "github.com/mercari/grpc-federation/grpc/federation;federation";
+option go_package = "github.com/mercari/grpc-federation/grpc/federation/cel;cel";
 
 // Error type information of the error variable used when evaluating CEL.
 message Error {
diff --git a/resolver/resolver.go b/resolver/resolver.go
index 44646735..b82a5723 100644
--- a/resolver/resolver.go
+++ b/resolver/resolver.go
@@ -3005,6 +3005,8 @@ func (r *Resolver) fromCELType(ctx *context, typ *cel.Type) (*Type, error) {
 	return nil, fmt.Errorf("unknown type %s is required", typ.TypeName())
 }
 
+const privateProtoFile = "grpc/federation/private.proto"
+
 func messageArgumentFileDescriptor(arg *Message) *descriptorpb.FileDescriptorProto {
 	desc := arg.File.Desc
 	msg := &descriptorpb.DescriptorProto{
@@ -3031,10 +3033,21 @@ func messageArgumentFileDescriptor(arg *Message) *descriptorpb.FileDescriptorPro
 			Label:    &label,
 		})
 	}
+	var importedPrivateFile bool
+	for _, dep := range desc.GetDependency() {
+		if dep == privateProtoFile {
+			importedPrivateFile = true
+			break
+		}
+	}
+	deps := append(desc.GetDependency(), arg.File.Name)
+	if !importedPrivateFile {
+		deps = append(deps, privateProtoFile)
+	}
 	return &descriptorpb.FileDescriptorProto{
 		Name:             proto.String(arg.Name),
 		Package:          proto.String(federation.PrivatePackageName),
-		Dependency:       append(desc.Dependency, arg.File.Name),
+		Dependency:       deps,
 		PublicDependency: desc.PublicDependency,
 		WeakDependency:   desc.WeakDependency,
 		MessageType:      []*descriptorpb.DescriptorProto{msg},