diff --git a/app/vmselect/promql/aggr_incremental.go b/app/vmselect/promql/aggr_incremental.go
index 4ae701b45..1392b270f 100644
--- a/app/vmselect/promql/aggr_incremental.go
+++ b/app/vmselect/promql/aggr_incremental.go
@@ -111,8 +111,8 @@ func (iafc *incrementalAggrFuncContext) updateTimeseries(tsOrig *timeseries, wor
 	removeGroupTags(&ts.MetricName, &iafc.ae.Modifier)
 	bb := bbPool.Get()
 	bb.B = marshalMetricNameSorted(bb.B[:0], &ts.MetricName)
-	k := string(bb.B)
-	iac := m[k]
+	k := bb.B
+	iac := m[string(k)]
 	if iac == nil {
 		if iafc.ae.Limit > 0 && len(m) >= iafc.ae.Limit {
 			// Skip this time series, since the limit on the number of output time series has been already reached.
@@ -131,7 +131,7 @@ func (iafc *incrementalAggrFuncContext) updateTimeseries(tsOrig *timeseries, wor
 			ts:     tsAggr,
 			values: make([]float64, len(ts.Values)),
 		}
-		m[k] = iac
+		m[string(k)] = iac
 	}
 	bbPool.Put(bb)
 	iafc.callbacks.updateAggrFunc(iac, ts.Values)