diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/AlarmHistorianRegistrationTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/AlarmHistorianRegistrationTests.cs
index de3b44a2..0d8db9a1 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/AlarmHistorianRegistrationTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/AlarmHistorianRegistrationTests.cs
@@ -152,6 +152,13 @@ public sealed class AlarmHistorianRegistrationTests
         opts.Validate().ShouldContain(w => w.Contains("Capacity"));
     }
 
+    [Fact]
+    public void Validate_warns_on_non_positive_retention()
+    {
+        var opts = new AlarmHistorianOptions { Enabled = true, SharedSecret = "s", DatabasePath = "/abs/h.db", DeadLetterRetentionDays = 0 };
+        opts.Validate().ShouldContain(w => w.Contains("DeadLetterRetentionDays"));
+    }
+
     [Fact]
     public void Validate_accumulates_multiple_warnings()
     {