diff --git a/reactos/include/psdk/winternl.h b/reactos/include/psdk/winternl.h
index 1496b0f7f1f..7f1a739b53d 100644
--- a/reactos/include/psdk/winternl.h
+++ b/reactos/include/psdk/winternl.h
@@ -1554,7 +1554,7 @@ typedef struct _KEY_MULTIPLE_VALUE_INFORMATION
   ULONG Type;
 } KEY_MULTIPLE_VALUE_INFORMATION, *PKEY_MULTIPLE_VALUE_INFORMATION;
 
-typedef VOID (*PTIMER_APC_ROUTINE) ( PVOID, ULONG, LONG );
+typedef VOID (CALLBACK *PTIMER_APC_ROUTINE) ( PVOID, ULONG, LONG );
 
 typedef enum _EVENT_TYPE {
   NotificationEvent,