diff --git a/reader.go b/reader.go
index 825f6922e..af3ba9105 100644
--- a/reader.go
+++ b/reader.go
@@ -889,13 +889,8 @@ func (r *Reader) Offset() int64 {
 	return offset
 }
 
-// Lag returns the lag of the last message returned by ReadMessage, or -1
-// if r is backed by a consumer group.
+// Lag returns the lag of the last message returned by ReadMessage or FetchMessage.
 func (r *Reader) Lag() int64 {
-	if r.useConsumerGroup() {
-		return -1
-	}
-
 	r.mutex.Lock()
 	lag := r.lag
 	r.mutex.Unlock()