diff --git a/weed/storage/needle_map/compact_map_test.go b/weed/storage/needle_map/compact_map_test.go
index 3bad85727..633be07f6 100644
--- a/weed/storage/needle_map/compact_map_test.go
+++ b/weed/storage/needle_map/compact_map_test.go
@@ -8,7 +8,14 @@ import (
 
 func TestOverflow2(t *testing.T) {
 	m := NewCompactMap()
-	m.Set(NeedleId(150088), ToOffset(8), 3000073)
+	_, oldSize := m.Set(NeedleId(150088), ToOffset(8), 3000073)
+	if oldSize!=0{
+		t.Fatalf("expecting no previous data")
+	}
+	_, oldSize = m.Set(NeedleId(150088), ToOffset(8), 3000073)
+	if oldSize!=3000073{
+		t.Fatalf("expecting previous data size is %d, not %d", 3000073, oldSize)
+	}
 	m.Set(NeedleId(150073), ToOffset(8), 3000073)
 	m.Set(NeedleId(150089), ToOffset(8), 3000073)
 	m.Set(NeedleId(150076), ToOffset(8), 3000073)