diff --git a/storage/fanout.go b/storage/fanout.go
index ae74ad2ca2..dd33999ebc 100644
--- a/storage/fanout.go
+++ b/storage/fanout.go
@@ -340,6 +340,9 @@ func (c *mergeSeriesSet) Next() bool {
 }
 
 func (c *mergeSeriesSet) At() Series {
+	if len(c.currentSets) == 1 {
+		return c.currentSets[0].At()
+	}
 	series := []Series{}
 	for _, seriesSet := range c.currentSets {
 		series = append(series, seriesSet.At())