diff --git a/wgpu-hal/src/dx12/mod.rs b/wgpu-hal/src/dx12/mod.rs
index 28556e96ee..9e1413f8d4 100644
--- a/wgpu-hal/src/dx12/mod.rs
+++ b/wgpu-hal/src/dx12/mod.rs
@@ -621,7 +621,7 @@ struct PassState {
 
 #[test]
 fn test_dirty_mask() {
-    assert_eq!(MAX_ROOT_ELEMENTS, mem::size_of::<u64>() * 8);
+    assert_eq!(MAX_ROOT_ELEMENTS, u64::BITS as usize);
 }
 
 impl PassState {