diff --git a/registry.go b/registry.go
index 4da4922..8f926b2 100644
--- a/registry.go
+++ b/registry.go
@@ -98,9 +98,13 @@ func (rr *rpcRegistry) Invoke(codec protocol.RegistryCodec) (result interface{},
 
 	if nil != methodSpec.returnType {
 		result = returnValues[0].Interface()
-		err = returnValues[1].Interface().(error)
+		if nil != returnValues[1].Interface() {
+			err = returnValues[1].Interface().(error)
+		}
 	} else {
-		err = returnValues[0].Interface().(error)
+		if nil != returnValues[0].Interface() {
+			err = returnValues[0].Interface().(error)
+		}
 	}
 
 	return