diff --git a/Content.Client/GameTicking/ClientGameTicker.cs b/Content.Client/GameTicking/ClientGameTicker.cs
index 3b58d1c17b..d618046255 100644
--- a/Content.Client/GameTicking/ClientGameTicker.cs
+++ b/Content.Client/GameTicking/ClientGameTicker.cs
@@ -26,6 +26,7 @@ namespace Content.Client.GameTicking
 
         [ViewVariables] public bool AreWeReady { get; private set; }
         [ViewVariables] public bool IsGameStarted { get; private set; }
+        [ViewVariables] public bool DisallowedLateJoin { get; private set; }
         [ViewVariables] public string ServerInfoBlob { get; private set; }
         [ViewVariables] public DateTime StartTime { get; private set; }
         [ViewVariables] public bool Paused { get; private set; }
@@ -34,6 +35,7 @@ namespace Content.Client.GameTicking
         public event Action InfoBlobUpdated;
         public event Action LobbyStatusUpdated;
         public event Action LobbyReadyUpdated;
+        public event Action LobbyLateJoinStatusUpdated;
 
         public void Initialize()
         {
@@ -50,11 +52,17 @@ namespace Content.Client.GameTicking
             {
                 IoCManager.Resolve<IClyde>().RequestWindowAttention();
             });
+            _netManager.RegisterNetMessage<MsgTickerLateJoinStatus>(nameof(MsgTickerLateJoinStatus), LateJoinStatus);
 
             Ready = new Dictionary<NetSessionId, bool>();
             _initialized = true;
         }
 
+        private void LateJoinStatus(MsgTickerLateJoinStatus message)
+        {
+            DisallowedLateJoin = message.Disallowed;
+            LobbyLateJoinStatusUpdated?.Invoke();
+        }
 
 
         private void JoinLobby(MsgTickerJoinLobby message)
diff --git a/Content.Client/Interfaces/IClientGameTicker.cs b/Content.Client/Interfaces/IClientGameTicker.cs
index 0bedce3995..e1e584e2f3 100644
--- a/Content.Client/Interfaces/IClientGameTicker.cs
+++ b/Content.Client/Interfaces/IClientGameTicker.cs
@@ -9,6 +9,7 @@ namespace Content.Client.Interfaces
         bool IsGameStarted { get; }
         string ServerInfoBlob { get; }
         bool AreWeReady { get; }
+        bool DisallowedLateJoin { get; }
         DateTime StartTime { get; }
         bool Paused { get; }
         Dictionary<NetSessionId, bool> Ready { get; }
@@ -17,5 +18,6 @@ namespace Content.Client.Interfaces
         event Action InfoBlobUpdated;
         event Action LobbyStatusUpdated;
         event Action LobbyReadyUpdated;
+        event Action LobbyLateJoinStatusUpdated;
     }
 }
diff --git a/Content.Client/State/LobbyState.cs b/Content.Client/State/LobbyState.cs
index b5fc2c35a1..2580dadb64 100644
--- a/Content.Client/State/LobbyState.cs
+++ b/Content.Client/State/LobbyState.cs
@@ -101,6 +101,7 @@ namespace Content.Client.State
             _clientGameTicker.InfoBlobUpdated += UpdateLobbyUi;
             _clientGameTicker.LobbyStatusUpdated += LobbyStatusUpdated;
             _clientGameTicker.LobbyReadyUpdated += LobbyReadyUpdated;
+            _clientGameTicker.LobbyLateJoinStatusUpdated += LobbyLateJoinStatusUpdated;
         }
 
         public override void Shutdown()
@@ -109,6 +110,7 @@ namespace Content.Client.State
             _clientGameTicker.InfoBlobUpdated -= UpdateLobbyUi;
             _clientGameTicker.LobbyStatusUpdated -= LobbyStatusUpdated;
             _clientGameTicker.LobbyReadyUpdated -= LobbyReadyUpdated;
+            _clientGameTicker.LobbyLateJoinStatusUpdated -= LobbyLateJoinStatusUpdated;
 
             _clientGameTicker.Ready.Clear();
 
@@ -173,6 +175,11 @@ namespace Content.Client.State
             UpdateLobbyUi();
         }
 
+        private void LobbyLateJoinStatusUpdated()
+        {
+            _lobby.ReadyButton.Disabled = _clientGameTicker.DisallowedLateJoin;
+        }
+
         private void UpdateLobbyUi()
         {
             if (_lobby == null)
@@ -191,6 +198,7 @@ namespace Content.Client.State
                 _lobby.StartTime.Text = "";
                 _lobby.ReadyButton.Text = Loc.GetString("Ready Up");
                 _lobby.ReadyButton.ToggleMode = true;
+                _lobby.ReadyButton.Disabled = false;
                 _lobby.ReadyButton.Pressed = _clientGameTicker.AreWeReady;
             }
 
diff --git a/Content.Server/GameTicking/GamePreset.cs b/Content.Server/GameTicking/GamePreset.cs
index 0e7ce86795..ddde553722 100644
--- a/Content.Server/GameTicking/GamePreset.cs
+++ b/Content.Server/GameTicking/GamePreset.cs
@@ -12,6 +12,7 @@ namespace Content.Server.GameTicking
         public abstract bool Start(IReadOnlyList<IPlayerSession> readyPlayers, bool force = false);
         public virtual string ModeTitle => "Sandbox";
         public virtual string Description => "Secret!";
+        public virtual bool DisallowLateJoin => false;
         public Dictionary<string, HumanoidCharacterProfile> readyProfiles;
     }
 }
diff --git a/Content.Server/GameTicking/GamePresets/PresetSuspicion.cs b/Content.Server/GameTicking/GamePresets/PresetSuspicion.cs
index 3ce23717d4..c77b8a110e 100644
--- a/Content.Server/GameTicking/GamePresets/PresetSuspicion.cs
+++ b/Content.Server/GameTicking/GamePresets/PresetSuspicion.cs
@@ -30,6 +30,9 @@ namespace Content.Server.GameTicking.GamePresets
         public int MinPlayers { get; set; } = 5;
         public int MinTraitors { get; set; } = 2;
         public int PlayersPerTraitor { get; set; } = 5;
+
+        public override bool DisallowLateJoin => true;
+
         private static string TraitorID = "SuspicionTraitor";
         private static string InnocentID = "SuspicionInnocent";
 
diff --git a/Content.Server/GameTicking/GameTicker.cs b/Content.Server/GameTicking/GameTicker.cs
index 476a7c55f8..34d40c8df3 100644
--- a/Content.Server/GameTicking/GameTicker.cs
+++ b/Content.Server/GameTicking/GameTicker.cs
@@ -94,6 +94,8 @@ namespace Content.Server.GameTicking
         [ViewVariables] private GameRunLevel _runLevel;
         [ViewVariables(VVAccess.ReadWrite)] private GridCoordinates _spawnPoint;
 
+        [ViewVariables] private bool DisallowLateJoin { get; set; } = false;
+
         [ViewVariables] private bool LobbyEnabled => _configurationManager.GetCVar<bool>("game.lobbyenabled");
 
         [ViewVariables] private bool _updateOnRoundEnd;
@@ -142,6 +144,7 @@ namespace Content.Server.GameTicking
             _netManager.RegisterNetMessage<MsgTickerLobbyReady>(nameof(MsgTickerLobbyReady));
             _netManager.RegisterNetMessage<MsgRoundEndMessage>(nameof(MsgRoundEndMessage));
             _netManager.RegisterNetMessage<MsgRequestWindowAttention>(nameof(MsgRequestWindowAttention));
+            _netManager.RegisterNetMessage<MsgTickerLateJoinStatus>(nameof(MsgTickerLateJoinStatus));
 
             SetStartPreset(_configurationManager.GetCVar<string>("game.defaultpreset"));
 
@@ -285,6 +288,8 @@ namespace Content.Server.GameTicking
             // Time to start the preset.
             var preset = MakeGamePreset(profiles);
 
+            DisallowLateJoin |= preset.DisallowLateJoin;
+
             if (!preset.Start(assignedJobs.Keys.ToList(), force))
             {
                 SetStartPreset(_configurationManager.GetCVar<string>("game.fallbackpreset"));
@@ -300,6 +305,13 @@ namespace Content.Server.GameTicking
             _roundStartTimeSpan = IoCManager.Resolve<IGameTiming>().RealTime;
             _sendStatusToAll();
             ReqWindowAttentionAll();
+            UpdateLateJoinStatus();
+        }
+
+        private void UpdateLateJoinStatus()
+        {
+            var msg = new MsgTickerLateJoinStatus(null) {Disallowed = DisallowLateJoin};
+            _netManager.ServerSendToAll(msg);
         }
 
         private void SendServerMessage(string message)
@@ -405,7 +417,7 @@ namespace Content.Server.GameTicking
 
             foreach (var rule in _gameRules)
             {
-                if (rule.GetType().Equals(t))
+                if (rule.GetType().IsAssignableFrom(t))
                     return true;
             }
 
@@ -637,7 +649,7 @@ namespace Content.Server.GameTicking
 
                 _playerJoinLobby(player);
             }
-            
+
             EntitySystem.Get<GasTileOverlaySystem>().ResettingCleanup();
             EntitySystem.Get<PathfindingSystem>().ResettingCleanup();
             EntitySystem.Get<AiReachableSystem>().ResettingCleanup();
@@ -646,6 +658,7 @@ namespace Content.Server.GameTicking
 
             _spawnedPositions.Clear();
             _manifest.Clear();
+            DisallowLateJoin = false;
         }
 
         private void _preRoundSetup()
@@ -776,6 +789,12 @@ namespace Content.Server.GameTicking
             string jobId = null,
             bool lateJoin = true)
         {
+            if (lateJoin && DisallowLateJoin)
+            {
+                MakeObserve(session);
+                return;
+            }
+
             _playerJoinGame(session);
 
             var data = session.ContentData();
diff --git a/Content.Shared/SharedGameTicker.cs b/Content.Shared/SharedGameTicker.cs
index d7100f93e4..e180ddb198 100644
--- a/Content.Shared/SharedGameTicker.cs
+++ b/Content.Shared/SharedGameTicker.cs
@@ -54,6 +54,31 @@ namespace Content.Shared
             }
         }
 
+        protected class MsgTickerLateJoinStatus : NetMessage
+        {
+            #region REQUIRED
+
+            public const MsgGroups GROUP = MsgGroups.Command;
+            public const string NAME = nameof(MsgTickerLateJoinStatus);
+
+            public bool Disallowed { get; set; }
+
+            public MsgTickerLateJoinStatus(INetChannel channel) : base(NAME, GROUP) { }
+
+            #endregion
+
+            public override void ReadFromBuffer(NetIncomingMessage buffer)
+            {
+                Disallowed = buffer.ReadBoolean();
+            }
+
+            public override void WriteToBuffer(NetOutgoingMessage buffer)
+            {
+                buffer.Write(Disallowed);
+            }
+        }
+
+
         protected class MsgTickerLobbyStatus : NetMessage
         {
             #region REQUIRED