diff --git a/SVSim.UnitTests/Controllers/FreeBattleControllerTests.cs b/SVSim.UnitTests/Controllers/FreeBattleControllerTests.cs
index 7dd8e46d..c0f3d5e8 100644
--- a/SVSim.UnitTests/Controllers/FreeBattleControllerTests.cs
+++ b/SVSim.UnitTests/Controllers/FreeBattleControllerTests.cs
@@ -93,4 +93,23 @@ public class FreeBattleControllerTests
         Assert.That(j3.GetProperty("matching_state").GetInt32(), Is.EqualTo(3007), "Owner = 3007.");
         Assert.That(j3.GetProperty("battle_id").GetString(), Is.EqualTo(j2.GetProperty("battle_id").GetString()));
     }
+
+    [Test]
+    public async Task DoMatching_returns_3001_when_viewer_has_no_deck_for_format_and_slot()
+    {
+        await using var factory = new SVSimTestFactory();
+        var viewerId = await factory.SeedViewerAsync();
+        await factory.SeedGlobalsAsync();
+        // Note: NO SeedDeckAsync. BuildForRankBattleAsync will throw InvalidOperationException.
+        var client = factory.CreateAuthenticatedClient(viewerId);
+
+        var resp = await client.PostAsJsonAsync("/unlimited_free_battle/do_matching", DoMatchingBody);
+
+        Assert.That(resp.IsSuccessStatusCode, Is.True);
+        using var doc = JsonDocument.Parse(await resp.Content.ReadAsStringAsync());
+        var data = doc.RootElement;
+        Assert.That(data.GetProperty("matching_state").GetInt32(), Is.EqualTo(3001),
+            "Missing deck → RC_BATTLE_MATCHING_ILLEGAL.");
+        Assert.That(data.GetProperty("node_server_url").GetString(), Is.EqualTo(""));
+    }
 }