diff --git a/OpenRA.Mods.Common/MapGenerator/MatrixUtils.cs b/OpenRA.Mods.Common/MapGenerator/MatrixUtils.cs
index 2d686002f5..f42c199a2d 100644
--- a/OpenRA.Mods.Common/MapGenerator/MatrixUtils.cs
+++ b/OpenRA.Mods.Common/MapGenerator/MatrixUtils.cs
@@ -1078,7 +1078,7 @@ namespace OpenRA.Mods.Common.MapGenerator
 				if (prop == FirstPassSentinel)
 					return chirality[point];
 
-				if (chirality[point] != 0)
+				if (chirality[point] != 0 || prop == 0)
 					return null;
 				chirality[point] = prop;
 				return prop;