diff --git a/SVSim.BattleNode/Bridge/MatchingBridge.cs b/SVSim.BattleNode/Bridge/MatchingBridge.cs
index e812714..0d7ed20 100644
--- a/SVSim.BattleNode/Bridge/MatchingBridge.cs
+++ b/SVSim.BattleNode/Bridge/MatchingBridge.cs
@@ -16,7 +16,8 @@ public sealed class MatchingBridge : IMatchingBridge
     public PendingMatch RegisterPendingBattle(long viewerId)
     {
         // 12-digit decimal battle id mirrors the captures (e.g. "975695075012").
-        var battleId = (Math.Abs(Guid.NewGuid().GetHashCode()) % 1_000_000_000_000L).ToString("D12");
+        // Cast to long before Math.Abs to avoid OverflowException on int.MinValue.
+        var battleId = (Math.Abs((long)Guid.NewGuid().GetHashCode()) % 1_000_000_000_000L).ToString("D12");
         _store.RegisterPending(new PendingBattle(battleId, viewerId));
         return new PendingMatch(battleId, _options.NodeServerUrl);
     }
diff --git a/SVSim.UnitTests/BattleNode/Bridge/MatchingBridgeTests.cs b/SVSim.UnitTests/BattleNode/Bridge/MatchingBridgeTests.cs
index 7dec521..c526ad1 100644
--- a/SVSim.UnitTests/BattleNode/Bridge/MatchingBridgeTests.cs
+++ b/SVSim.UnitTests/BattleNode/Bridge/MatchingBridgeTests.cs
@@ -32,4 +32,15 @@ public class MatchingBridgeTests
 
         Assert.That(a.BattleId, Is.Not.EqualTo(b.BattleId));
     }
+
+    [Test]
+    public void RegisterPendingBattle_ProducesTwelveDigitDecimalBattleId()
+    {
+        var bridge = new MatchingBridge(new InMemoryBattleSessionStore(), new BattleNodeOptions());
+
+        var match = bridge.RegisterPendingBattle(viewerId: 1);
+
+        Assert.That(match.BattleId, Has.Length.EqualTo(12));
+        Assert.That(match.BattleId, Does.Match("^[0-9]{12}$"));
+    }
 }