diff --git a/sdk/include/psdk/mmsystem.h b/sdk/include/psdk/mmsystem.h
index b3b2347c890..08221ad0a10 100644
--- a/sdk/include/psdk/mmsystem.h
+++ b/sdk/include/psdk/mmsystem.h
@@ -999,7 +999,7 @@ typedef struct DRVCONFIGINFOEX {
 } DRVCONFIGINFOEX,*PDRVCONFIGINFOEX,*LPDRVCONFIGINFOEX;
 
 typedef LRESULT (CALLBACK* DRIVERPROC)(DWORD_PTR,HDRVR,UINT,LPARAM,LPARAM);
-typedef void (CALLBACK DRVCALLBACK)(HDRVR,UINT,DWORD,DWORD,DWORD);
+typedef void (CALLBACK DRVCALLBACK)(HDRVR, UINT, DWORD_PTR, DWORD_PTR, DWORD_PTR);
 typedef DRVCALLBACK *LPDRVCALLBACK;
 typedef DRVCALLBACK *PDRVCALLBACK;
 DECLARE_HANDLE(HWAVE);