diff --git a/pkg/store/bucket.go b/pkg/store/bucket.go
index e2c68576ce9..2d56a9680e8 100644
--- a/pkg/store/bucket.go
+++ b/pkg/store/bucket.go
@@ -824,7 +824,7 @@ type blockSeriesClient struct {
 	chunkFetchDuration prometheus.Histogram
 
 	// Internal state.
-	i               int
+	i               uint64
 	postings        []storage.SeriesRef
 	chkMetas        []chunks.Meta
 	lset            labels.Labels