diff --git a/pkg/store/storepb/testutil/series.go b/pkg/store/storepb/testutil/series.go
index 083eb5d9d51..f2b58072b18 100644
--- a/pkg/store/storepb/testutil/series.go
+++ b/pkg/store/storepb/testutil/series.go
@@ -72,6 +72,10 @@ func CreateHeadWithSeries(t testing.TB, j int, opts HeadGenOptions) (*tsdb.Head,
 	if opts.ScrapeInterval == 0 {
 		opts.ScrapeInterval = 1 * time.Millisecond
 	}
+	// Use float type if sample type is not set.
+	if opts.SampleType == chunkenc.ValNone {
+		opts.SampleType = chunkenc.ValFloat
+	}
 
 	fmt.Printf(
 		"Creating %d %d-sample series with %s interval in %s\n",