diff --git a/irc/channel.go b/irc/channel.go
index 59a80a04..d444de74 100644
--- a/irc/channel.go
+++ b/irc/channel.go
@@ -1256,7 +1256,7 @@ func (channel *Channel) isMuted(client *Client) bool {
 	if muteRe == nil {
 		return false
 	}
-	nuh := client.NickMaskString()
+	nuh := client.NickMaskCasefolded()
 	return muteRe.MatchString(nuh) && !channel.lists[modes.ExceptMask].MatchMute(nuh)
 }