diff --git a/ch4-rpc/ch4-01-rpc-intro.md b/ch4-rpc/ch4-01-rpc-intro.md
index 84fc2f3..c033b86 100644
--- a/ch4-rpc/ch4-01-rpc-intro.md
+++ b/ch4-rpc/ch4-01-rpc-intro.md
@@ -73,7 +73,7 @@ func main() {
 ```go
 const HelloServiceName = "path/to/pkg.HelloService"
 
-type HelloServiceInterface = interface {
+type HelloServiceInterface interface {
 	Hello(request string, reply *string) error
 }