diff --git a/internal/rootcoord/quota_center.go b/internal/rootcoord/quota_center.go
index 5f63f5e355..cd5960b90d 100644
--- a/internal/rootcoord/quota_center.go
+++ b/internal/rootcoord/quota_center.go
@@ -454,13 +454,13 @@ func (q *QuotaCenter) calculateWriteRates() error {
 func (q *QuotaCenter) getTimeTickDelayFactor(ts Timestamp) map[int64]float64 {
 	log := log.Ctx(context.Background()).WithRateGroup("rootcoord.QuotaCenter", 1.0, 60.0)
 	if !Params.QuotaConfig.TtProtectionEnabled.GetAsBool() {
-		return nil
+		return make(map[int64]float64)
 	}
 
 	maxDelay := Params.QuotaConfig.MaxTimeTickDelay.GetAsDuration(time.Second)
 	if maxDelay < 0 {
 		// < 0 means disable tt protection
-		return nil
+		return make(map[int64]float64)
 	}
 
 	collectionsMaxDelay := make(map[int64]time.Duration)
@@ -526,7 +526,7 @@ func (q *QuotaCenter) getTimeTickDelayFactor(ts Timestamp) map[int64]float64 {
 func (q *QuotaCenter) getMemoryFactor() map[int64]float64 {
 	log := log.Ctx(context.Background()).WithRateGroup("rootcoord.QuotaCenter", 1.0, 60.0)
 	if !Params.QuotaConfig.MemProtectionEnabled.GetAsBool() {
-		return nil
+		return make(map[int64]float64)
 	}
 
 	dataNodeMemoryLowWaterLevel := Params.QuotaConfig.DataNodeMemoryLowWaterLevel.GetAsFloat()
diff --git a/internal/rootcoord/quota_center_test.go b/internal/rootcoord/quota_center_test.go
index a972a525f3..ca5ab2a529 100644
--- a/internal/rootcoord/quota_center_test.go
+++ b/internal/rootcoord/quota_center_test.go
@@ -320,7 +320,7 @@ func TestQuotaCenter(t *testing.T) {
 		assert.NoError(t, err)
 
 		// force deny
-		forceBak := Params.QuotaConfig.ForceDenyWriting
+		forceBak := Params.QuotaConfig.ForceDenyWriting.GetValue()
 		paramtable.Get().Save(Params.QuotaConfig.ForceDenyWriting.Key, "true")
 		quotaCenter.writableCollections = []int64{1, 2, 3}
 		quotaCenter.resetAllCurrentRates()
@@ -330,7 +330,22 @@ func TestQuotaCenter(t *testing.T) {
 			assert.Equal(t, Limit(0), quotaCenter.currentRates[collection][internalpb.RateType_DMLInsert])
 			assert.Equal(t, Limit(0), quotaCenter.currentRates[collection][internalpb.RateType_DMLDelete])
 		}
-		Params.QuotaConfig.ForceDenyWriting = forceBak
+		paramtable.Get().Save(Params.QuotaConfig.ForceDenyWriting.Key, forceBak)
+
+		// disable tt delay protection
+		disableTtBak := Params.QuotaConfig.TtProtectionEnabled.GetValue()
+		paramtable.Get().Save(Params.QuotaConfig.TtProtectionEnabled.Key, "false")
+		quotaCenter.resetAllCurrentRates()
+		quotaCenter.queryNodeMetrics = make(map[UniqueID]*metricsinfo.QueryNodeQuotaMetrics)
+		quotaCenter.queryNodeMetrics[0] = &metricsinfo.QueryNodeQuotaMetrics{
+			Hms: metricsinfo.HardwareMetrics{
+				Memory:      100,
+				MemoryUsage: 100,
+			},
+			Effect: metricsinfo.NodeEffect{CollectionIDs: []int64{1, 2, 3}},
+		}
+		err = quotaCenter.calculateWriteRates()
+		paramtable.Get().Save(Params.QuotaConfig.TtProtectionEnabled.Key, disableTtBak)
 	})
 
 	t.Run("test MemoryFactor factors", func(t *testing.T) {