diff --git a/OpenRA.Game/Map/Map.cs b/OpenRA.Game/Map/Map.cs
index 25d30212e9..4724884176 100644
--- a/OpenRA.Game/Map/Map.cs
+++ b/OpenRA.Game/Map/Map.cs
@@ -61,7 +61,6 @@ namespace OpenRA
 		public bool? Creeps;
 		public bool? AllyBuildRadius;
 		public string TechLevel;
-		public bool ConfigurableStartingUnits = true;
 		public string[] Difficulties = { };
 		public bool? ShortGame;
 
@@ -118,7 +117,6 @@ namespace OpenRA
 		public string Description;
 		public string Author;
 		public string Tileset;
-		public bool AllowStartUnitConfig = true;
 		public Bitmap CustomPreview;
 		public bool InvalidCustomRules { get; private set; }
 
diff --git a/OpenRA.Game/Network/Session.cs b/OpenRA.Game/Network/Session.cs
index dbb6e48341..3eb3ea5267 100644
--- a/OpenRA.Game/Network/Session.cs
+++ b/OpenRA.Game/Network/Session.cs
@@ -191,7 +191,7 @@ namespace OpenRA.Network
 			public bool AllyBuildRadius = true;
 			public int StartingCash = 5000;
 			public string TechLevel = "none";
-			public string StartingUnitsClass = "none";
+			public string StartingUnitsClass;
 			public string GameSpeedType = "default";
 			public bool ShortGame = true;
 			public bool AllowVersionMismatch;
diff --git a/OpenRA.Mods.Common/ServerTraits/LobbyCommands.cs b/OpenRA.Mods.Common/ServerTraits/LobbyCommands.cs
index f9070afb67..03f84d407b 100644
--- a/OpenRA.Mods.Common/ServerTraits/LobbyCommands.cs
+++ b/OpenRA.Mods.Common/ServerTraits/LobbyCommands.cs
@@ -617,7 +617,8 @@ namespace OpenRA.Mods.Common.Server
 							return true;
 						}
 
-						if (!server.Map.Options.ConfigurableStartingUnits)
+						var startingUnits = server.Map.Rules.Actors["world"].TraitInfoOrDefault<SpawnMPUnitsInfo>();
+						if (startingUnits == null || startingUnits.Locked)
 						{
 							server.SendOrderTo(conn, "Message", "Map has disabled start unit configuration.");
 							return true;
@@ -1030,6 +1031,9 @@ namespace OpenRA.Mods.Common.Server
 			var resources = server.Map.Rules.Actors["player"].TraitInfo<PlayerResourcesInfo>();
 			gs.StartingCash = resources.DefaultCash;
 
+			var startingUnits = server.Map.Rules.Actors["world"].TraitInfoOrDefault<SpawnMPUnitsInfo>();
+			gs.StartingUnitsClass = startingUnits == null ? "none" : startingUnits.StartingUnitsClass;
+
 			server.Map.Options.UpdateServerSettings(server.LobbyInfo.GlobalSettings);
 		}
 
diff --git a/OpenRA.Mods.Common/Traits/World/SpawnMPUnits.cs b/OpenRA.Mods.Common/Traits/World/SpawnMPUnits.cs
index c4f461ae40..3bbc5e5e02 100644
--- a/OpenRA.Mods.Common/Traits/World/SpawnMPUnits.cs
+++ b/OpenRA.Mods.Common/Traits/World/SpawnMPUnits.cs
@@ -18,7 +18,13 @@ using OpenRA.Traits;
 namespace OpenRA.Mods.Common.Traits
 {
 	[Desc("Spawn base actor at the spawnpoint and support units in an annulus around the base actor. Both are defined at MPStartUnits. Attach this to the world actor.")]
-	public class SpawnMPUnitsInfo : TraitInfo<SpawnMPUnits>, Requires<MPStartLocationsInfo>, Requires<MPStartUnitsInfo> { }
+	public class SpawnMPUnitsInfo : TraitInfo<SpawnMPUnits>, Requires<MPStartLocationsInfo>, Requires<MPStartUnitsInfo>
+	{
+		public readonly string StartingUnitsClass = "none";
+
+		[Desc("Prevent the starting units option from being changed in the lobby.")]
+		public bool Locked = false;
+	}
 
 	public class SpawnMPUnits : IWorldLoaded
 	{
diff --git a/OpenRA.Mods.Common/Widgets/Logic/Lobby/LobbyLogic.cs b/OpenRA.Mods.Common/Widgets/Logic/Lobby/LobbyLogic.cs
index e44aeaa6be..7b52a6cb8d 100644
--- a/OpenRA.Mods.Common/Widgets/Logic/Lobby/LobbyLogic.cs
+++ b/OpenRA.Mods.Common/Widgets/Logic/Lobby/LobbyLogic.cs
@@ -429,19 +429,27 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 			var startingUnits = optionsBin.GetOrNull<DropDownButtonWidget>("STARTINGUNITS_DROPDOWNBUTTON");
 			if (startingUnits != null)
 			{
-				var startUnitsInfo = modRules.Actors["world"].TraitInfos<MPStartUnitsInfo>();
-				var classes = startUnitsInfo.Select(a => a.Class).Distinct();
+				var startUnitsInfos = new CachedTransform<Map, IEnumerable<MPStartUnitsInfo>>(
+					map => map.Rules.Actors["world"].TraitInfos<MPStartUnitsInfo>());
+
+				var startUnitsLocked = new CachedTransform<Map, bool>(map =>
+				{
+					var spawnUnitsInfo = map.Rules.Actors["world"].TraitInfoOrDefault<SpawnMPUnitsInfo>();
+					return spawnUnitsInfo == null || spawnUnitsInfo.Locked;
+				});
+
 				Func<string, string> className = c =>
 				{
-					var selectedClass = startUnitsInfo.Where(s => s.Class == c).Select(u => u.ClassName).FirstOrDefault();
+					var selectedClass = startUnitsInfos.Update(Map).Where(s => s.Class == c).Select(u => u.ClassName).FirstOrDefault();
 					return selectedClass != null ? selectedClass : c;
 				};
 
-				startingUnits.IsDisabled = () => configurationDisabled() || !Map.Options.ConfigurableStartingUnits;
+				startingUnits.IsDisabled = () => configurationDisabled() || startUnitsLocked.Update(Map);
 				startingUnits.GetText = () => MapPreview.Status != MapStatus.Available ||
-					Map == null || !Map.Options.ConfigurableStartingUnits ? "Not Available" : className(orderManager.LobbyInfo.GlobalSettings.StartingUnitsClass);
+					Map == null || startUnitsLocked.Update(Map) ? "Not Available" : className(orderManager.LobbyInfo.GlobalSettings.StartingUnitsClass);
 				startingUnits.OnMouseDown = _ =>
 				{
+					var classes = startUnitsInfos.Update(Map).Select(a => a.Class).Distinct();
 					var options = classes.Select(c => new DropDownOption
 					{
 						Title = className(c),
diff --git a/mods/cnc/mod.yaml b/mods/cnc/mod.yaml
index 0277b7c4ac..eac9c02431 100644
--- a/mods/cnc/mod.yaml
+++ b/mods/cnc/mod.yaml
@@ -163,7 +163,6 @@ ServerTraits:
 	LobbySettingsNotification
 
 LobbyDefaults:
-	StartingUnitsClass: light
 	TechLevel: Unrestricted
 
 ChromeMetrics:
diff --git a/mods/cnc/rules/world.yaml b/mods/cnc/rules/world.yaml
index 5ff347d8eb..4006d6c919 100644
--- a/mods/cnc/rules/world.yaml
+++ b/mods/cnc/rules/world.yaml
@@ -135,6 +135,7 @@ World:
 		BaseActor: mcv
 		SupportActors: e1,e1,e1,e1,e1,e2,e2,e2,e3,e3,apc,mtnk
 	SpawnMPUnits:
+		StartingUnitsClass: light
 	CrateSpawner:
 		Minimum: 1
 		Maximum: 6