diff --git a/include/d3d11.idl b/include/d3d11.idl
index eef826f5251..e472944c97c 100644
--- a/include/d3d11.idl
+++ b/include/d3d11.idl
@@ -445,6 +445,8 @@ typedef enum D3D11_INPUT_CLASSIFICATION
     D3D11_INPUT_PER_INSTANCE_DATA,
 } D3D11_INPUT_CLASSIFICATION;
 
+const UINT D3D11_APPEND_ALIGNED_ELEMENT = 0xffffffff;
+
 typedef struct D3D11_INPUT_ELEMENT_DESC
 {
     LPCSTR SemanticName;