diff --git a/lib/storage/storage_test.go b/lib/storage/storage_test.go
index ca165d4ba..27129b325 100644
--- a/lib/storage/storage_test.go
+++ b/lib/storage/storage_test.go
@@ -988,7 +988,7 @@ func testStorageAddRows(rng *rand.Rand, s *Storage) error {
 	const addsCount = 10
 
 	maxTimestamp := timestampFromTime(time.Now())
-	minTimestamp := maxTimestamp - s.retentionMsecs
+	minTimestamp := maxTimestamp - s.retentionMsecs + 3600*1000
 	for i := 0; i < addsCount; i++ {
 		mrs := testGenerateMetricRows(rng, rowsPerAdd, minTimestamp, maxTimestamp)
 		if err := s.AddRows(mrs, defaultPrecisionBits); err != nil {
@@ -1030,7 +1030,9 @@ func testStorageAddRows(rng *rand.Rand, s *Storage) error {
 		return fmt.Errorf("snapshot %q must contain at least %d rows; got %d", snapshotPath, minRowsExpected, rowsCount)
 	}
 
-	// Verify that force merge for the snapshot leaves only a single part per partition.
+	// Verify that force merge for the snapshot leaves at most a single part per partition.
+	// Zero parts are possible if the snapshot is created just after the partition has been created
+	// by concurrent goroutine, but it didn't put the data into it yet.
 	if err := s1.ForceMergePartitions(""); err != nil {
 		return fmt.Errorf("error when force merging partitions: %w", err)
 	}
@@ -1039,9 +1041,9 @@ func testStorageAddRows(rng *rand.Rand, s *Storage) error {
 		pws := ptw.pt.GetParts(nil, true)
 		numParts := len(pws)
 		ptw.pt.PutParts(pws)
-		if numParts != 1 {
+		if numParts > 1 {
 			s1.tb.PutPartitions(ptws)
-			return fmt.Errorf("unexpected number of parts for partition %q after force merge; got %d; want 1", ptw.pt.name, numParts)
+			return fmt.Errorf("unexpected number of parts for partition %q after force merge; got %d; want at most 1", ptw.pt.name, numParts)
 		}
 	}
 	s1.tb.PutPartitions(ptws)