diff --git a/README.md b/README.md
index 6b72c98..a9d7c70 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,15 @@
 
 ![image](https://raw.githubusercontent.com/ysugimoto/grpc-graphql-gateway/master/misc/grpc-graphql-gateway.png)
 
+## Change Log
+
+### v0.9.1
+
+#### Changed middleware fucntion type
+
+On MiddlewareFunc, you need to return `context.Context` as first return value. this is because we need to make custom metadata to gRPC on middleware process.
+If you are already using your onw middleware, plase change its interface. see https://github.com/ysugimoto/grpc-graphql-gateway/pull/10
+
 ## Motivation
 
 On API development, frequently we choose some IDL, in order to manage API definitions from a file.
diff --git a/runtime/middlewares.go b/runtime/middlewares.go
index cfd1822..3096083 100644
--- a/runtime/middlewares.go
+++ b/runtime/middlewares.go
@@ -7,11 +7,11 @@ import (
 
 // Cors is middelware function to provide CORS headers to response headers
 func Cors() MiddlewareFunc {
-	return func(ctx context.Context, w http.ResponseWriter, r *http.Request) error {
+	return func(ctx context.Context, w http.ResponseWriter, r *http.Request) (context.Context, error) {
 		w.Header().Set("Access-Control-Allow-Origin", r.URL.Host)
 		w.Header().Set("Access-Control-Allow-Credentials", "true")
 		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, OPTIONS")
 		w.Header().Set("Access-Control-Max-Age", "1728000")
-		return nil
+		return ctx, nil
 	}
 }
diff --git a/runtime/mux.go b/runtime/mux.go
index 68466d1..ead9c15 100644
--- a/runtime/mux.go
+++ b/runtime/mux.go
@@ -14,7 +14,7 @@ import (
 
 type (
 	// MiddlewareFunc type definition
-	MiddlewareFunc func(ctx context.Context, w http.ResponseWriter, r *http.Request) error
+	MiddlewareFunc func(ctx context.Context, w http.ResponseWriter, r *http.Request) (context.Context, error)
 
 	// Custom error handler which is called on graphql result has an error
 	GraphqlErrorHandler func(errs gqlerrors.FormattedErrors)
@@ -92,9 +92,10 @@ func (s *ServeMux) Use(ms ...MiddlewareFunc) *ServeMux {
 // ServeHTTP implements http.Handler
 func (s *ServeMux) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	ctx := r.Context()
-
 	for _, m := range s.middlewares {
-		if err := m(ctx, w, r); err != nil {
+		var err error
+		ctx, err = m(ctx, w, r)
+		if err != nil {
 			http.Error(w, "middleware error occurred: "+err.Error(), http.StatusInternalServerError)
 			return
 		}