diff --git a/dlls/winmm/mmio.c b/dlls/winmm/mmio.c
index 5491fc22c87..0bf8d4092c0 100644
--- a/dlls/winmm/mmio.c
+++ b/dlls/winmm/mmio.c
@@ -44,6 +44,8 @@
 
 WINE_DEFAULT_DEBUG_CHANNEL(mmio);
 
+LRESULT         (*pFnMmioCallback16)(SEGPTR,LPMMIOINFO,UINT,LPARAM,LPARAM) /* = NULL */;
+
 /**************************************************************************
  *               	mmioDosIOProc           		[internal]
  */
@@ -71,9 +73,7 @@ static LRESULT CALLBACK mmioDosIOProc(LPMMIOINFO lpmmioinfo, UINT uMessage,
 	    }
 
 	    /* if filename NULL, assume open file handle in adwInfo[0] */
-	    if (!szFileName) {
-                lpmmioinfo->adwInfo[0] = DosFileHandleToWin32Handle(lpmmioinfo->adwInfo[0]);
-	    } else {
+	    if (szFileName) {
                 OFSTRUCT    ofs;
                 lpmmioinfo->adwInfo[0] = (DWORD)OpenFile(szFileName, &ofs, lpmmioinfo->dwFlags & 0xFFFF);
             }
@@ -352,9 +352,9 @@ static LRESULT	send_message(struct IOProcList* ioProc, LPMMIOINFO mmioinfo,
 
     switch (ioProc->type) {
     case MMIO_PROC_16:
-        if (WINMM_IData && WINMM_IData->pFnMmioCallback16)
-            result = WINMM_IData->pFnMmioCallback16((SEGPTR)ioProc->pIOProc,
-                                                    mmioinfo, wMsg, lp1, lp2);
+        if (pFnMmioCallback16)
+            result = pFnMmioCallback16((SEGPTR)ioProc->pIOProc,
+                                       mmioinfo, wMsg, lp1, lp2);
         break;
     case MMIO_PROC_32A:
     case MMIO_PROC_32W:
@@ -579,9 +579,6 @@ static MMRESULT MMIO_SetBuffer(WINE_MMIO* wm, void* pchBuffer, LONG cchBuffer,
 	wm->info.pchBuffer = NULL;
     }
 
-    if (wm->ioProc->type == MMIO_PROC_16)
-        wm->info.dwReserved1 = MapLS(wm->info.pchBuffer);
-
     wm->info.cchBuffer = cchBuffer;
     wm->info.pchNext = wm->info.pchBuffer;
     wm->info.pchEndRead = wm->info.pchBuffer;
diff --git a/dlls/winmm/mmsystem.c b/dlls/winmm/mmsystem.c
index 96d9c131b5b..43171b09891 100644
--- a/dlls/winmm/mmsystem.c
+++ b/dlls/winmm/mmsystem.c
@@ -49,9 +49,7 @@ extern LONG CALLBACK MMSYSTEM_CallTo16_long_l    (FARPROC16,LONG);
 extern LONG CALLBACK MMSYSTEM_CallTo16_long_lwll (LPMMIOPROC16,LONG,WORD,LONG,LONG);
 /* ### stop build ### */
 
-static LRESULT CALLBACK mmioCallback16(SEGPTR cb16,
-                                       LPMMIOINFO lpmmioinfo, UINT uMessage,
-                                       LPARAM lParam1, LPARAM lParam2);
+static LRESULT          MMIO_Callback16(SEGPTR, LPMMIOINFO, UINT, LPARAM, LPARAM);
 
 /* ###################################################
  * #                  LIBRARY                        #
@@ -85,10 +83,12 @@ BOOL WINAPI MMSYSTEM_LibMain(DWORD fdwReason, HINSTANCE hinstDLL, WORD ds,
 	}
 	WINMM_IData->hWinMM16Instance = hinstDLL;
 	WINMM_IData->h16Module32 = hndl;
-        WINMM_IData->pFnMmioCallback16 = mmioCallback16;
+        /* hook in our 16 bit function pointers */
+        pFnMmioCallback16 = MMIO_Callback16;
 	break;
     case DLL_PROCESS_DETACH:
 	FreeLibrary(WINMM_IData->h16Module32);
+        pFnMmioCallback16 = NULL;
 	break;
     case DLL_THREAD_ATTACH:
     case DLL_THREAD_DETACH:
@@ -2511,13 +2511,12 @@ static LRESULT	MMIO_UnMap32To16(DWORD wMsg, LPARAM lParam1, LPARAM lParam2,
 }
 
 /******************************************************************
- *		mmioCallback16
+ *		MMIO_Callback16
  *
  *
  */
-static LRESULT CALLBACK mmioCallback16(SEGPTR cb16,
-                                       LPMMIOINFO lpmmioinfo, UINT uMessage,
-                                       LPARAM lParam1, LPARAM lParam2)
+static LRESULT MMIO_Callback16(SEGPTR cb16, LPMMIOINFO lpmmioinfo, UINT uMessage,
+                               LPARAM lParam1, LPARAM lParam2)
 {
     LRESULT 		result;
     MMIOINFO16          mmioInfo16;
@@ -2552,8 +2551,6 @@ static LRESULT CALLBACK mmioCallback16(SEGPTR cb16,
 /******************************************************************
  *             MMIO_ResetSegmentedData
  *
- * 
- * 
  */
 static LRESULT     MMIO_SetSegmentedBuffer(HMMIO hmmio, SEGPTR ptr)
 {
@@ -2583,7 +2580,10 @@ HMMIO16 WINAPI mmioOpen16(LPSTR szFileName, MMIOINFO16* lpmmioinfo16,
 	mmioinfo.pIOProc     = (LPMMIOPROC)lpmmioinfo16->pIOProc;
 	mmioinfo.cchBuffer   = lpmmioinfo16->cchBuffer;
 	mmioinfo.pchBuffer   = MapSL((DWORD)lpmmioinfo16->pchBuffer);
-	mmioinfo.adwInfo[0]  = lpmmioinfo16->adwInfo[0];
+        mmioinfo.adwInfo[0]  = lpmmioinfo16->adwInfo[0];
+        /* if we don't have a file name, it's likely a passed open file descriptor */
+        if (!szFileName) 
+            mmioinfo.adwInfo[0] = DosFileHandleToWin32Handle(mmioinfo.adwInfo[0]);
 	mmioinfo.adwInfo[1]  = lpmmioinfo16->adwInfo[1];
 	mmioinfo.adwInfo[2]  = lpmmioinfo16->adwInfo[2];
 	mmioinfo.adwInfo[3]  = lpmmioinfo16->adwInfo[3];
diff --git a/dlls/winmm/winemm.h b/dlls/winmm/winemm.h
index e6d5d9295b3..6a58f0291a5 100644
--- a/dlls/winmm/winemm.h
+++ b/dlls/winmm/winemm.h
@@ -217,7 +217,6 @@ typedef struct tagWINE_MM_IDATA {
     /* LPWINE_MIXER		lpMixer; */
     /* mmio part */
     LPWINE_MMIO			lpMMIO;
-    LRESULT (CALLBACK*          pFnMmioCallback16)(SEGPTR,LPMMIOINFO,UINT,LPARAM,LPARAM);
     /* playsound and sndPlaySound */
     WINE_PLAYSOUND*             lpPlaySound;
     HANDLE                      psLastEvent;
@@ -341,6 +340,11 @@ BOOL	MMDRV_GetDescription16(const char* fname, char* buf, int buflen);
 /* Global variables */
 extern LPWINE_MM_IDATA		WINMM_IData;
 
+/* pointers to 16 bit functions (if sibling MMSYSTEM.DLL is loaded
+ * NULL otherwise
+ */
+extern LRESULT         (*pFnMmioCallback16)(SEGPTR,LPMMIOINFO,UINT,LPARAM,LPARAM);
+
 /* HANDLE16 -> HANDLE conversions */
 #define HDRVR_32(h16)		((HDRVR)(ULONG_PTR)(h16))
 #define HMIDI_32(h16)		((HMIDI)(ULONG_PTR)(h16))