diff --git a/SVSim.UnitTests/RoutingSmokeTests.cs b/SVSim.UnitTests/RoutingSmokeTests.cs
index 7b3dc7e1..e78f761b 100644
--- a/SVSim.UnitTests/RoutingSmokeTests.cs
+++ b/SVSim.UnitTests/RoutingSmokeTests.cs
@@ -52,6 +52,22 @@ public class RoutingSmokeTests
             "SpecialTitleCheck should return the built-in title id \"0\".");
     }
 
+    [Test]
+    public async Task ImmutableDataCardMaster_resolves_to_ImmutableDataController()
+    {
+        using var factory = new TestFactory();
+        using var client = factory.CreateClient();
+
+        var response = await client.PostAsync("/immutable_data/card_master",
+            new StringContent(ValidBaseRequestJson, Encoding.UTF8, "application/json"));
+
+        // [Authorize] on SVSimController means an unauthenticated POST returns 401 — that still
+        // proves routing resolved (404 would mean the path didn't bind).
+        Assert.That((int)response.StatusCode, Is.Not.EqualTo((int)HttpStatusCode.NotFound),
+            $"Expected /immutable_data/card_master to route; got 404. Body: " +
+            await response.Content.ReadAsStringAsync());
+    }
+
     [Test]
     public async Task ImportViewer_route_resolves()
     {