diff --git a/pkg/query/iter.go b/pkg/query/iter.go
index 9a107144908..bd58127168e 100644
--- a/pkg/query/iter.go
+++ b/pkg/query/iter.go
@@ -582,6 +582,7 @@ func (it *dedupSeriesIterator) Next() bool {
 	// Advance both iterators to at least the next highest timestamp plus the potential penalty.
 	if it.aok {
 		it.aok = it.a.Seek(it.lastT + 1 + it.penA)
+		// When A is exhausted the seek for B below should be without any penalty
 		if !it.aok {
 			it.penB = 0
 		}