diff --git a/grpc.go b/grpc.go
index ef0c9be..f230fa4 100644
--- a/grpc.go
+++ b/grpc.go
@@ -8,7 +8,6 @@ import (
 	"net"
 	"reflect"
 	"strings"
-	"sync"
 	"sync/atomic"
 	"time"
 
@@ -25,11 +24,9 @@ import (
 )
 
 type grpcClient struct {
-	opts   client.Options
-	codecs map[string]encoding.Codec
-	pool   *pool
-	once   atomic.Value
-	sync.RWMutex
+	opts client.Options
+	pool *pool
+	once atomic.Value
 }
 
 func init() {
@@ -304,13 +301,18 @@ func (g *grpcClient) maxSendMsgSizeValue() int {
 }
 
 func (g *grpcClient) newGRPCCodec(contentType string) (encoding.Codec, error) {
-	g.RLock()
-	defer g.RUnlock()
-
-	if c, ok := g.codecs[contentType]; ok {
+	codecs := make(map[string]encoding.Codec)
+	if g.opts.Context != nil {
+		if v := g.opts.Context.Value(codecsKey{}); v != nil {
+			codecs = v.(map[string]encoding.Codec)
+		}
+	}
+	if c, ok := codecs[contentType]; ok {
+		return wrapCodec{c}, nil
+	}
+	if c, ok := defaultGRPCCodecs[contentType]; ok {
 		return wrapCodec{c}, nil
 	}
-
 	return nil, fmt.Errorf("Unsupported Content-Type: %s", contentType)
 }
 
@@ -719,22 +721,6 @@ func newClient(opts ...client.Option) client.Client {
 		c = options.Wrappers[i-1](c)
 	}
 
-	rc.codecs = make(map[string]encoding.Codec, len(defaultGRPCCodecs))
-	for k, v := range defaultGRPCCodecs {
-		rc.codecs[k] = v
-	}
-
-	var codecs map[string]encoding.Codec
-	if rc.opts.Context != nil {
-		if v := rc.opts.Context.Value(codecsKey{}); v != nil {
-			codecs = v.(map[string]encoding.Codec)
-		}
-	}
-
-	for k, v := range codecs {
-		rc.codecs[k] = v
-	}
-
 	return c
 }