diff --git a/src/ZB.MOM.WW.ScadaBridge.SiteRuntime/SiteRuntimeOptionsValidator.cs b/src/ZB.MOM.WW.ScadaBridge.SiteRuntime/SiteRuntimeOptionsValidator.cs
index 8de19199..e34ef736 100644
--- a/src/ZB.MOM.WW.ScadaBridge.SiteRuntime/SiteRuntimeOptionsValidator.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.SiteRuntime/SiteRuntimeOptionsValidator.cs
@@ -56,5 +56,14 @@ public sealed class SiteRuntimeOptionsValidator : OptionsValidatorBase<SiteRunti
         builder.RequireThat(options.ConfigFetchRetryCount >= 0,
             $"ScadaBridge:SiteRuntime:ConfigFetchRetryCount must be >= 0 " +
             $"(was {options.ConfigFetchRetryCount}).");
+
+        builder.RequireThat(options.TagSubscribeRetryIntervalMs > 0,
+            $"ScadaBridge:SiteRuntime:TagSubscribeRetryIntervalMs must be greater than 0 " +
+            $"(was {options.TagSubscribeRetryIntervalMs}); a zero interval hot-loops the tag-subscribe " +
+            "retry and a negative one throws inside the Instance Actor's retry scheduling.");
+
+        builder.RequireThat(options.StuckScriptGraceMs >= 0,
+            $"ScadaBridge:SiteRuntime:StuckScriptGraceMs must be >= 0 " +
+            $"(was {options.StuckScriptGraceMs}); a negative grace throws inside the stuck-script watchdog's delay.");
     }
 }
diff --git a/tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/SiteRuntimeOptionsValidatorTests.cs b/tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/SiteRuntimeOptionsValidatorTests.cs
index e8bbf54e..1d627316 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/SiteRuntimeOptionsValidatorTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/SiteRuntimeOptionsValidatorTests.cs
@@ -40,6 +40,24 @@ public class SiteRuntimeOptionsValidatorTests
         Assert.Contains("ScriptExecutionThreadCount", result.FailureMessage);
     }
 
+    [Fact]
+    public void ZeroTagSubscribeRetryIntervalMs_IsRejected()
+    {
+        var result = Validate(new SiteRuntimeOptions { TagSubscribeRetryIntervalMs = 0 });
+
+        Assert.True(result.Failed);
+        Assert.Contains("TagSubscribeRetryIntervalMs", result.FailureMessage);
+    }
+
+    [Fact]
+    public void NegativeStuckScriptGraceMs_IsRejected()
+    {
+        var result = Validate(new SiteRuntimeOptions { StuckScriptGraceMs = -1 });
+
+        Assert.True(result.Failed);
+        Assert.Contains("StuckScriptGraceMs", result.FailureMessage);
+    }
+
     [Fact]
     public void ZeroStreamBufferSize_IsRejected()
     {