diff --git a/pkg/receive/writer.go b/pkg/receive/writer.go
index 90bb2897c4c..f76cd44ee41 100644
--- a/pkg/receive/writer.go
+++ b/pkg/receive/writer.go
@@ -77,8 +77,11 @@ func (r *Writer) Write(ctx context.Context, tenantID string, wreq *prompb.WriteR
 		if ref == 0 {
 			// If not, copy labels, as TSDB will hold those strings long term. Given no
 			// copy unmarshal we don't want to keep memory for whole protobuf, only for labels.
-			labelpb.ReAllocZLabelsStrings(&t.Labels)
-			lset = labelpb.ZLabelsToPromLabels(t.Labels)
+			lsetCopy := make([]labelpb.ZLabel, len(t.Labels))
+			copy(lsetCopy, t.Labels)
+
+			labelpb.ReAllocZLabelsStrings(&lsetCopy)
+			lset = labelpb.ZLabelsToPromLabels(lsetCopy)
 		}
 
 		// Append as many valid samples as possible, but keep track of the errors.