diff --git a/metrics_batcher.go b/metrics_batcher.go
index 54a92e9..3b8bb3c 100644
--- a/metrics_batcher.go
+++ b/metrics_batcher.go
@@ -52,7 +52,7 @@ func (mb *metricsBatcher) addTimeSeries(ts *monitoringpb.TimeSeries) {
 			Name:       monitoring.MetricProjectPath(mb.projectID),
 			TimeSeries: mb.allTss,
 		})
-		mb.allTss = make([]*monitoringpb.TimeSeries, maxTimeSeriesPerUpload)
+		mb.allTss = make([]*monitoringpb.TimeSeries, 0, maxTimeSeriesPerUpload)
 	}
 }