diff --git a/ch4-rpc/ch4-02-pb-intro.md b/ch4-rpc/ch4-02-pb-intro.md
index af73e50..92ba7d0 100644
--- a/ch4-rpc/ch4-02-pb-intro.md
+++ b/ch4-rpc/ch4-02-pb-intro.md
@@ -354,7 +354,7 @@ type {{.ServiceName}}Interface interface {
 	{{- end}}
 }
 
-func Register{{.ServiceName}}(srv *rpc.Server, x {{.ServiceName}}) error {
+func Register{{.ServiceName}}(srv *rpc.Server, x {{.ServiceName}}Interface) error {
 	if err := srv.RegisterName("{{.ServiceName}}", x); err != nil {
 		return err
 	}
diff --git a/vendor/gobook.examples/ch4-02-proto/protoc-gen-go-netrpc/netprpc.go b/vendor/gobook.examples/ch4-02-proto/protoc-gen-go-netrpc/netprpc.go
index 790eaf3..27c5dcd 100644
--- a/vendor/gobook.examples/ch4-02-proto/protoc-gen-go-netrpc/netprpc.go
+++ b/vendor/gobook.examples/ch4-02-proto/protoc-gen-go-netrpc/netprpc.go
@@ -87,7 +87,7 @@ type {{.ServiceName}}Interface interface {
 	{{- end}}
 }
 
-func Register{{.ServiceName}}(srv *rpc.Server, x {{.ServiceName}}) error {
+func Register{{.ServiceName}}(srv *rpc.Server, x {{.ServiceName}}Interface) error {
 	if err := srv.RegisterName("{{.ServiceName}}", x); err != nil {
 		return err
 	}