diff --git a/OpenRA.Game/Traits/Render/RenderBuildingWarFactory.cs b/OpenRA.Game/Traits/Render/RenderBuildingWarFactory.cs
index 053ba3b9a3..969fba8f4c 100644
--- a/OpenRA.Game/Traits/Render/RenderBuildingWarFactory.cs
+++ b/OpenRA.Game/Traits/Render/RenderBuildingWarFactory.cs
@@ -53,7 +53,7 @@ namespace OpenRA.Traits
 		public void Tick(Actor self)
 		{
 			if (isOpen && !self.World.WorldActor.traits.Get<UnitInfluence>()
-				.GetUnitsAt(((1/24f) * self.CenterLocation).ToInt2()).Any())
+				.GetUnitsAt(((1f/Game.CellSize) * self.CenterLocation).ToInt2()).Any())
 			{
 				isOpen = false;
 				roof.PlayBackwardsThen(GetPrefix(self) + "build-top", () => roof.Play(GetPrefix(self) + "idle-top"));
diff --git a/OpenRA.Game/Traits/World/UnitInfluence.cs b/OpenRA.Game/Traits/World/UnitInfluence.cs
index a3be7ef6a6..afaba57b49 100644
--- a/OpenRA.Game/Traits/World/UnitInfluence.cs
+++ b/OpenRA.Game/Traits/World/UnitInfluence.cs
@@ -22,6 +22,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using OpenRA.FileFormats;
 
 namespace OpenRA.Traits
 {
@@ -33,10 +34,12 @@ namespace OpenRA.Traits
 	public class UnitInfluence : ITick
 	{
 		List<Actor>[,] influence;
+		Map map;
 
 		public UnitInfluence( Actor self )
 		{
-			int size = self.World.Map.MapSize;
+			map = self.World.Map;
+			var size = self.World.Map.MapSize;
 			influence = new List<Actor>[size, size];
 			for (int i = 0; i < size; i++)
 				for (int j = 0; j < size; j++)
@@ -90,6 +93,7 @@ namespace OpenRA.Traits
 
 		public IEnumerable<Actor> GetUnitsAt( int2 a )
 		{
+			if (!map.IsInMap(a)) return null;
 			return influence[ a.X, a.Y ];
 		}