diff --git a/OpenRA.Mods.Common/Lint/CheckMapMetadata.cs b/OpenRA.Mods.Common/Lint/CheckMapMetadata.cs
index 28a3d8b48f..7eb83c41d2 100644
--- a/OpenRA.Mods.Common/Lint/CheckMapMetadata.cs
+++ b/OpenRA.Mods.Common/Lint/CheckMapMetadata.cs
@@ -31,6 +31,9 @@ namespace OpenRA.Mods.Common.Lint
 
 			if (!map.Categories.Any())
 				emitError("Map does not define any categories.");
+
+			if (map.InvalidCustomRules)
+				emitError("Map contains invalid custom rules.");
 		}
 	}
 }
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