diff --git a/k8s/monitoring/database-alerts.yaml b/k8s/monitoring/database-alerts.yaml
index 4a9c4f2e..9142fac1 100644
--- a/k8s/monitoring/database-alerts.yaml
+++ b/k8s/monitoring/database-alerts.yaml
@@ -149,7 +149,7 @@ spec:
         # -----------------------------------------------------------------
         - alert: RedisMemoryHigh
           expr: |
-            redis_memory_used_bytes / redis_memory_max_bytes > 0.85
+            redis_memory_max_bytes > 0 and redis_memory_used_bytes / redis_memory_max_bytes > 0.85
           for: 5m
           labels:
             severity: warning
diff --git a/ops/monitoring/alerts-unified.yml b/ops/monitoring/alerts-unified.yml
index 025e9c7d..4d44c551 100644
--- a/ops/monitoring/alerts-unified.yml
+++ b/ops/monitoring/alerts-unified.yml
@@ -193,7 +193,7 @@ groups:
           description: "當前連接數 {{ $value }} 超過 80"
 
       - alert: RedisMemoryHigh
-        expr: redis_memory_used_bytes / redis_memory_max_bytes * 100 > 80
+        expr: redis_memory_max_bytes > 0 and redis_memory_used_bytes / redis_memory_max_bytes * 100 > 80
         for: 5m
         labels:
           severity: warning