diff --git a/metadata.go b/metadata.go
index 197dc49..bb69743 100644
--- a/metadata.go
+++ b/metadata.go
@@ -10,23 +10,23 @@ import (
 
 type wrapper struct {
 	client.Client
-	exclude []string
+	keys []string
 }
 
-func NewClientWrapper(exclude ...string) client.Wrapper {
+func NewClientWrapper(keys ...string) client.Wrapper {
 	return func(c client.Client) client.Client {
 		handler := &wrapper{
-			Client:  c,
-			exclude: exclude,
+			Client: c,
+			keys:   keys,
 		}
 		return handler
 	}
 }
 
-func NewClientCallWrapper(exclude ...string) client.CallWrapper {
+func NewClientCallWrapper(keys ...string) client.CallWrapper {
 	return func(fn client.CallFunc) client.CallFunc {
 		return func(ctx context.Context, addr string, req client.Request, rsp interface{}, opts client.CallOptions) error {
-			if exclude == nil {
+			if keys == nil {
 				return fn(ctx, addr, req, rsp, opts)
 			}
 			if imd, iok := metadata.FromIncomingContext(ctx); iok && imd != nil {
@@ -34,7 +34,14 @@ func NewClientCallWrapper(exclude ...string) client.CallWrapper {
 				if !ook || omd == nil {
 					omd = metadata.New(len(imd))
 				}
-				ctx = metadata.NewOutgoingContext(ctx, metadata.Merge(omd, metadata.Copy(imd, exclude...), false))
+				for _, k := range keys {
+					if v, ok := imd.Get(k); ok && v != "" {
+						omd.Set(k, v)
+					}
+				}
+				if !ook {
+					ctx = metadata.NewOutgoingContext(ctx, omd)
+				}
 			}
 			return fn(ctx, addr, req, rsp, opts)
 		}
@@ -42,7 +49,7 @@ func NewClientCallWrapper(exclude ...string) client.CallWrapper {
 }
 
 func (w *wrapper) Call(ctx context.Context, req client.Request, rsp interface{}, opts ...client.CallOption) error {
-	if w.exclude == nil {
+	if w.keys == nil {
 		return w.Client.Call(ctx, req, rsp, opts...)
 	}
 	if imd, iok := metadata.FromIncomingContext(ctx); iok && imd != nil {
@@ -50,13 +57,20 @@ func (w *wrapper) Call(ctx context.Context, req client.Request, rsp interface{},
 		if !ook || omd == nil {
 			omd = metadata.New(len(imd))
 		}
-		ctx = metadata.NewOutgoingContext(ctx, metadata.Merge(omd, metadata.Copy(imd, w.exclude...), false))
+		for _, k := range w.keys {
+			if v, ok := imd.Get(k); ok && v != "" {
+				omd.Set(k, v)
+			}
+		}
+		if !ook {
+			ctx = metadata.NewOutgoingContext(ctx, omd)
+		}
 	}
 	return w.Client.Call(ctx, req, rsp, opts...)
 }
 
 func (w *wrapper) Stream(ctx context.Context, req client.Request, opts ...client.CallOption) (client.Stream, error) {
-	if w.exclude == nil {
+	if w.keys == nil {
 		return w.Client.Stream(ctx, req, opts...)
 	}
 	if imd, iok := metadata.FromIncomingContext(ctx); iok && imd != nil {
@@ -64,15 +78,22 @@ func (w *wrapper) Stream(ctx context.Context, req client.Request, opts ...client
 		if !ook || omd == nil {
 			omd = metadata.New(len(imd))
 		}
-		ctx = metadata.NewOutgoingContext(ctx, metadata.Merge(omd, metadata.Copy(imd, w.exclude...), false))
+		for _, k := range w.keys {
+			if v, ok := imd.Get(k); ok && v != "" {
+				omd.Set(k, v)
+			}
+		}
+		if !ook {
+			ctx = metadata.NewOutgoingContext(ctx, omd)
+		}
 	}
 	return w.Client.Stream(ctx, req, opts...)
 }
 
-func NewServerHandlerWrapper(exclude ...string) server.HandlerWrapper {
+func NewServerHandlerWrapper(keys ...string) server.HandlerWrapper {
 	return func(fn server.HandlerFunc) server.HandlerFunc {
 		return func(ctx context.Context, req server.Request, rsp interface{}) error {
-			if exclude == nil {
+			if keys == nil {
 				return fn(ctx, req, rsp)
 			}
 			if imd, iok := metadata.FromIncomingContext(ctx); iok && imd != nil {
@@ -80,7 +101,14 @@ func NewServerHandlerWrapper(exclude ...string) server.HandlerWrapper {
 				if !ook || omd == nil {
 					omd = metadata.New(len(imd))
 				}
-				ctx = metadata.NewOutgoingContext(ctx, metadata.Merge(omd, metadata.Copy(imd, exclude...), false))
+				for _, k := range keys {
+					if v, ok := imd.Get(k); ok && v != "" {
+						omd.Set(k, v)
+					}
+				}
+				if !ook {
+					ctx = metadata.NewOutgoingContext(ctx, omd)
+				}
 			}
 			return fn(ctx, req, rsp)
 		}