diff --git a/OpenRA.Game/Network/Order.cs b/OpenRA.Game/Network/Order.cs
index 04b12b7bbc..dd8f390d63 100644
--- a/OpenRA.Game/Network/Order.cs
+++ b/OpenRA.Game/Network/Order.cs
@@ -72,7 +72,7 @@ namespace OpenRA
 						var subjectId = r.ReadUInt32();
 						var flags = (OrderFields)r.ReadByte();
 
-						var targetActorId = flags.HasField(OrderFields.TargetActor) ? r.ReadUInt32() : 0xffffffff;
+						var targetActorId = flags.HasField(OrderFields.TargetActor) ? r.ReadUInt32() : uint.MaxValue;
 						var targetLocation = (CPos)(flags.HasField(OrderFields.TargetLocation) ? r.ReadInt2() : int2.Zero);
 						var targetString = flags.HasField(OrderFields.TargetString) ? r.ReadString() : null;
 						var queued = flags.HasField(OrderFields.Queued);
@@ -104,28 +104,20 @@ namespace OpenRA
 
 		static uint UIntFromActor(Actor a)
 		{
-			if (a == null) return 0xffffffff;
+			if (a == null) return uint.MaxValue;
 			return a.ActorID;
 		}
 
 		static bool TryGetActorFromUInt(World world, uint aID, out Actor ret)
 		{
-			if (aID == 0xFFFFFFFF)
+			if (aID == uint.MaxValue)
 			{
 				ret = null;
 				return true;
 			}
-			else
-			{
-				foreach (var a in world.Actors.Where(x => x.ActorID == aID))
-				{
-					ret = a;
-					return true;
-				}
 
-				ret = null;
-				return false;
-			}
+			ret = world.GetActorById(aID);
+			return ret != null;
 		}
 
 		// Named constructors for Orders.
diff --git a/OpenRA.Game/World.cs b/OpenRA.Game/World.cs
index 94ce263507..1eca349fec 100644
--- a/OpenRA.Game/World.cs
+++ b/OpenRA.Game/World.cs
@@ -26,15 +26,8 @@ namespace OpenRA
 
 	public sealed class World : IDisposable
 	{
-		class ActorIDComparer : IComparer<Actor>
-		{
-			public static readonly ActorIDComparer Instance = new ActorIDComparer();
-			ActorIDComparer() { }
-			public int Compare(Actor x, Actor y) { return x.ActorID.CompareTo(y.ActorID); }
-		}
-
 		internal readonly TraitDictionary TraitDict = new TraitDictionary();
-		readonly SortedSet<Actor> actors = new SortedSet<Actor>(ActorIDComparer.Instance);
+		readonly SortedDictionary<uint, Actor> actors = new SortedDictionary<uint, Actor>();
 		readonly List<IEffect> effects = new List<IEffect>();
 		readonly Queue<Action<World>> frameEndActions = new Queue<Action<World>>();
 
@@ -225,7 +218,7 @@ namespace OpenRA
 		public void Add(Actor a)
 		{
 			a.IsInWorld = true;
-			actors.Add(a);
+			actors.Add(a.ActorID, a);
 			ActorAdded(a);
 
 			foreach (var t in a.TraitsImplementing<INotifyAddedToWorld>())
@@ -235,7 +228,7 @@ namespace OpenRA
 		public void Remove(Actor a)
 		{
 			a.IsInWorld = false;
-			actors.Remove(a);
+			actors.Remove(a.ActorID);
 			ActorRemoved(a);
 
 			foreach (var t in a.TraitsImplementing<INotifyRemovedFromWorld>())
@@ -283,7 +276,7 @@ namespace OpenRA
 							ni.Trait.TickIdle(ni.Actor);
 
 				using (new PerfSample("tick_activities"))
-					foreach (var a in actors)
+					foreach (var a in actors.Values)
 						a.Tick();
 
 				ActorsWithTrait<ITick>().DoTimed(x => x.Trait.Tick(x.Actor), "Trait");
@@ -301,9 +294,17 @@ namespace OpenRA
 			ActorsWithTrait<ITickRender>().DoTimed(x => x.Trait.TickRender(wr, x.Actor), "Render");
 		}
 
-		public IEnumerable<Actor> Actors { get { return actors; } }
+		public IEnumerable<Actor> Actors { get { return actors.Values; } }
 		public IEnumerable<IEffect> Effects { get { return effects; } }
 
+		public Actor GetActorById(uint actorId)
+		{
+			Actor a;
+			if (actors.TryGetValue(actorId, out a))
+				return a;
+			return null;
+		}
+
 		uint nextAID = 0;
 		internal uint NextAID()
 		{
@@ -367,7 +368,7 @@ namespace OpenRA
 			Sound.StopVideo();
 
 			// Dispose newer actors first, and the world actor last
-			foreach (var a in actors.Reverse())
+			foreach (var a in actors.Values.Reverse())
 				a.Dispose();
 
 			// Actor disposals are done in a FrameEndTask
diff --git a/OpenRA.Mods.Common/Traits/Player/ActorGroupProxy.cs b/OpenRA.Mods.Common/Traits/Player/ActorGroupProxy.cs
index 55987fe1ea..174d26fe39 100644
--- a/OpenRA.Mods.Common/Traits/Player/ActorGroupProxy.cs
+++ b/OpenRA.Mods.Common/Traits/Player/ActorGroupProxy.cs
@@ -26,7 +26,7 @@ namespace OpenRA.Mods.Common.Traits
 				/* create a group */
 				var actors = order.TargetString.Split(',')
 					.Select(id => uint.Parse(id, NumberStyles.Any, NumberFormatInfo.InvariantInfo))
-					.Select(id => self.World.Actors.FirstOrDefault(a => a.ActorID == id))
+					.Select(id => self.World.GetActorById(id))
 						.Where(a => a != null);
 
 				new Group(actors);