diff --git a/app/vmselect/netstorage/netstorage.go b/app/vmselect/netstorage/netstorage.go
index 1e1cfcb9f..0afe04a9e 100644
--- a/app/vmselect/netstorage/netstorage.go
+++ b/app/vmselect/netstorage/netstorage.go
@@ -1217,7 +1217,7 @@ func SearchMetricNames(qt *querytracer.Tracer, denyPartialResponse bool, sq *sto
 		return nil, isPartial, fmt.Errorf("cannot fetch metric names from vmstorage nodes: %w", err)
 	}
 
-	metricNames := make([]string, len(metricNamesMap))
+	metricNames := make([]string, 0, len(metricNamesMap))
 	for metricName := range metricNamesMap {
 		metricNames = append(metricNames, metricName)
 	}
diff --git a/app/vmselect/prometheus/series_response.qtpl b/app/vmselect/prometheus/series_response.qtpl
index 6ebbb1f08..5357747b7 100644
--- a/app/vmselect/prometheus/series_response.qtpl
+++ b/app/vmselect/prometheus/series_response.qtpl
@@ -15,7 +15,7 @@ See https://prometheus.io/docs/prometheus/latest/querying/api/#finding-series-by
 		{% for i, metricName := range metricNames %}
 			{% code err := mn.UnmarshalString(metricName) %}
 			{% if err != nil %}
-				{%q= err.Error() %}
+				{%q= "cannot unmarshal metricName: " + err.Error() %}
 			{% else %}
 				{%= metricNameObject(&mn) %}
 			{% endif %}
diff --git a/app/vmselect/prometheus/series_response.qtpl.go b/app/vmselect/prometheus/series_response.qtpl.go
index ee79b7094..a4fd400b9 100644
--- a/app/vmselect/prometheus/series_response.qtpl.go
+++ b/app/vmselect/prometheus/series_response.qtpl.go
@@ -52,7 +52,7 @@ func StreamSeriesResponse(qw422016 *qt422016.Writer, isPartial bool, metricNames
 //line app/vmselect/prometheus/series_response.qtpl:17
 		if err != nil {
 //line app/vmselect/prometheus/series_response.qtpl:18
-			qw422016.N().Q(err.Error())
+			qw422016.N().Q("cannot unmarshal metricName: " + err.Error())
 //line app/vmselect/prometheus/series_response.qtpl:19
 		} else {
 //line app/vmselect/prometheus/series_response.qtpl:20