diff --git a/OpenRA.Game/Map/Map.cs b/OpenRA.Game/Map/Map.cs
index 98d57d3147..896a28a94c 100644
--- a/OpenRA.Game/Map/Map.cs
+++ b/OpenRA.Game/Map/Map.cs
@@ -336,9 +336,6 @@ namespace OpenRA
 				throw new InvalidDataException($"Map format {MapFormat} is not supported.\n File: {package.Name}");
 
 			PlayerDefinitions = MiniYaml.NodesOrEmpty(yaml, "Players");
-			if (PlayerDefinitions.Count > 64)
-				throw new InvalidDataException($"Maps must not define more than 64 players.\n File: {package.Name}");
-
 			ActorDefinitions = MiniYaml.NodesOrEmpty(yaml, "Actors");
 
 			Grid = modData.Manifest.Get<MapGrid>();
diff --git a/OpenRA.Game/Map/MapPlayers.cs b/OpenRA.Game/Map/MapPlayers.cs
index 49ad3fdc1a..d048f9eb4a 100644
--- a/OpenRA.Game/Map/MapPlayers.cs
+++ b/OpenRA.Game/Map/MapPlayers.cs
@@ -17,6 +17,10 @@ namespace OpenRA
 {
 	public class MapPlayers
 	{
+		// Player masks are represented using a 64 bit integer
+		// The "Everyone" player for spectators is created at runtime,
+		// reducing the available player count for maps by 1.
+		public const int MaximumPlayerCount = 63;
 		public readonly Dictionary<string, PlayerReference> Players;
 
 		public MapPlayers()
diff --git a/OpenRA.Game/Server/MapStatusCache.cs b/OpenRA.Game/Server/MapStatusCache.cs
index 65f40fa42c..89cb2dff17 100644
--- a/OpenRA.Game/Server/MapStatusCache.cs
+++ b/OpenRA.Game/Server/MapStatusCache.cs
@@ -88,6 +88,12 @@ namespace OpenRA.Server
 					status = Session.MapStatus.Incompatible;
 				}
 
+				if (map.Players.Players.Count > MapPlayers.MaximumPlayerCount)
+				{
+					Log.Write("server", "Failed to load `{0}`: Player count exceeds maximum ({1}/{2}).", map.Title, map.Players.Players.Count, MapPlayers.MaximumPlayerCount);
+					status = Session.MapStatus.Incompatible;
+				}
+
 				cache[map] = status;
 
 				if ((status & Session.MapStatus.Validating) != 0)
diff --git a/OpenRA.Mods.Common/Widgets/Logic/Ingame/IngameMenuLogic.cs b/OpenRA.Mods.Common/Widgets/Logic/Ingame/IngameMenuLogic.cs
index b561662d7f..9522536315 100644
--- a/OpenRA.Mods.Common/Widgets/Logic/Ingame/IngameMenuLogic.cs
+++ b/OpenRA.Mods.Common/Widgets/Logic/Ingame/IngameMenuLogic.cs
@@ -351,12 +351,27 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 				hideMenu = true;
 				var editorActorLayer = world.WorldActor.Trait<EditorActorLayer>();
 				var actionManager = world.WorldActor.Trait<EditorActionManager>();
+
+				var playerDefinitions = editorActorLayer.Players.ToMiniYaml();
+
+				var playerCount = new MapPlayers(playerDefinitions).Players.Count;
+				if (playerCount > MapPlayers.MaximumPlayerCount)
+				{
+					ConfirmationDialogs.ButtonPrompt(
+						title: "Error: Max player count exceeded",
+						text: $"There are too many players defined ({playerCount}/{MapPlayers.MaximumPlayerCount}).",
+						onConfirm: ShowMenu,
+						confirmText: "Back");
+
+					return;
+				}
+
 				Ui.OpenWindow("SAVE_MAP_PANEL", new WidgetArgs()
 				{
 					{ "onSave", (Action<string>)(_ => { hideMenu = false; actionManager.Modified = false; }) },
 					{ "onExit", () => hideMenu = false },
 					{ "map", world.Map },
-					{ "playerDefinitions", editorActorLayer.Players.ToMiniYaml() },
+					{ "playerDefinitions", playerDefinitions },
 					{ "actorDefinitions", editorActorLayer.Save() }
 				});
 			};