diff --git a/p2p/discv5/net.go b/p2p/discv5/net.go
index 9b0bd0c80a..4c39c05533 100644
--- a/p2p/discv5/net.go
+++ b/p2p/discv5/net.go
@@ -1228,7 +1228,7 @@ func (net *Network) checkTopicRegister(data *topicRegister) (*pong, error) {
 	if rlpHash(data.Topics) != pongpkt.data.(*pong).TopicHash {
 		return nil, errors.New("topic hash mismatch")
 	}
-	if data.Idx < 0 || int(data.Idx) >= len(data.Topics) {
+	if int(data.Idx) < 0 || int(data.Idx) >= len(data.Topics) {
 		return nil, errors.New("topic index out of range")
 	}
 	return pongpkt.data.(*pong), nil