diff --git a/OpenRA.Mods.Common/Traits/Render/WithVoxelBody.cs b/OpenRA.Mods.Common/Traits/Render/WithVoxelBody.cs
index ea840465b4..0f44be7fae 100644
--- a/OpenRA.Mods.Common/Traits/Render/WithVoxelBody.cs
+++ b/OpenRA.Mods.Common/Traits/Render/WithVoxelBody.cs
@@ -39,7 +39,7 @@ namespace OpenRA.Mods.Common.Traits
 
 	public class WithVoxelBody : IAutoSelectionSize
 	{
-		int2 size;
+		readonly int2 size;
 
 		public WithVoxelBody(Actor self, WithVoxelBodyInfo info)
 		{