diff --git a/pkg/store/storepb/testutil/series.go b/pkg/store/storepb/testutil/series.go
index dc3f88325ad..7a03af7272d 100644
--- a/pkg/store/storepb/testutil/series.go
+++ b/pkg/store/storepb/testutil/series.go
@@ -16,20 +16,18 @@ import (
 	"time"
 
 	"github.com/cespare/xxhash"
-	"github.com/prometheus/prometheus/model/histogram"
-	"github.com/prometheus/prometheus/storage"
-	"github.com/prometheus/prometheus/tsdb/chunkenc"
-	"github.com/stretchr/testify/require"
-	"go.uber.org/atomic"
-
+	"github.com/efficientgo/core/testutil"
 	"github.com/gogo/protobuf/types"
+	"github.com/prometheus/prometheus/model/histogram"
 	"github.com/prometheus/prometheus/model/labels"
+	"github.com/prometheus/prometheus/storage"
 	"github.com/prometheus/prometheus/tsdb"
+	"github.com/prometheus/prometheus/tsdb/chunkenc"
 	"github.com/prometheus/prometheus/tsdb/chunks"
 	"github.com/prometheus/prometheus/tsdb/index"
 	"github.com/prometheus/prometheus/tsdb/wlog"
-
-	"github.com/efficientgo/core/testutil"
+	"github.com/stretchr/testify/require"
+	"go.uber.org/atomic"
 
 	"github.com/thanos-io/thanos/pkg/store/hintspb"
 	"github.com/thanos-io/thanos/pkg/store/labelpb"
@@ -72,6 +70,10 @@ 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",