diff --git a/include/winternl.h b/include/winternl.h
index fe77359680c..d38f49cde07 100644
--- a/include/winternl.h
+++ b/include/winternl.h
@@ -1782,7 +1782,7 @@ typedef struct _KEY_MULTIPLE_VALUE_INFORMATION
 
 typedef VOID (CALLBACK *PRTL_OVERLAPPED_COMPLETION_ROUTINE)(DWORD,DWORD,LPVOID);
 
-typedef VOID (*PTIMER_APC_ROUTINE) ( PVOID, ULONG, LONG );
+typedef VOID (CALLBACK *PTIMER_APC_ROUTINE) ( PVOID, ULONG, LONG );
 
 typedef enum _EVENT_TYPE {
   NotificationEvent,