diff --git a/windows/class.c b/windows/class.c
index 2ea1161..c4c467e 100644
--- a/windows/class.c
+++ b/windows/class.c
@@ -461,7 +461,7 @@
  *	>0: Unique identifier
  *	0: Failure
  */
-ATOM WINAPI RegisterClassA( const WNDCLASSA* wc ) /* Address of structure with class data */
+ATOM WINAPI RegisterClassA( const WNDCLASSA* wc ) /* [in] Address of structure with class data */
 {
     ATOM atom;
     int iSmIconWidth, iSmIconHeight;