diff --git a/protocol/dubbo/codec.go b/protocol/dubbo/codec.go
index 4e7e5ec0a0ecf341c16643c3d745e78398a9f28a..6b41d5e7d76d31ea23f08b77c841d0f87986bef7 100644
--- a/protocol/dubbo/codec.go
+++ b/protocol/dubbo/codec.go
@@ -90,6 +90,8 @@ func (p *DubboPackage) Unmarshal(buf *bytes.Buffer, opts ...interface{}) error {
 		}
 
 		if p.Header.Type&hessian.PackageRequest != 0x00 {
+			// size of this array must be '7'
+			// https://github.com/apache/dubbo-go-hessian2/blob/master/request.go#L272
 			p.Body = make([]interface{}, 7)
 		} else {
 			pendingRsp, ok := client.pendingResponses.Load(SequenceType(p.Header.ID))