diff --git a/dlls/winmm/winmm.c b/dlls/winmm/winmm.c
index 0f3cd5d..1412d5e 100644
--- a/dlls/winmm/winmm.c
+++ b/dlls/winmm/winmm.c
@@ -413,12 +413,12 @@ static	LPWINE_MIDI	MIDI_OutAlloc(HMIDIOUT* lphMidiOut, DWORD_PTR* lpdwCallback,
 /**************************************************************************
  * 				midiOutOpen    		[WINMM.@]
  */
-UINT WINAPI midiOutOpen(LPHMIDIOUT lphMidiOut, UINT uDeviceID,
+MMRESULT WINAPI midiOutOpen(LPHMIDIOUT lphMidiOut, UINT uDeviceID,
                        DWORD_PTR dwCallback, DWORD_PTR dwInstance, DWORD dwFlags)
 {
     HMIDIOUT		hMidiOut;
     LPWINE_MIDI		lpwm;
-    UINT		dwRet;
+    MMRESULT		dwRet;
 
     TRACE("(%p, %d, %08lX, %08lX, %08X);\n",
 	  lphMidiOut, uDeviceID, dwCallback, dwInstance, dwFlags);
@@ -699,12 +699,12 @@ UINT WINAPI midiInGetDevCapsA(UINT_PTR uDeviceID, LPMIDIINCAPSA lpCaps, UINT uSi
 /**************************************************************************
  * 				midiInOpen		[WINMM.@]
  */
-UINT WINAPI midiInOpen(HMIDIIN* lphMidiIn, UINT uDeviceID,
+MMRESULT WINAPI midiInOpen(HMIDIIN* lphMidiIn, UINT uDeviceID,
 		       DWORD_PTR dwCallback, DWORD_PTR dwInstance, DWORD dwFlags)
 {
     HANDLE		hMidiIn;
     LPWINE_MIDI		lpwm;
-    DWORD		dwRet;
+    MMRESULT		dwRet;
 
     TRACE("(%p, %d, %08lX, %08lX, %08X);\n",
 	  lphMidiIn, uDeviceID, dwCallback, dwInstance, dwFlags);
diff --git a/include/mmsystem.h b/include/mmsystem.h
index f53f11d..721e5e6 100644
--- a/include/mmsystem.h
+++ b/include/mmsystem.h
@@ -778,7 +778,7 @@ UINT		WINAPI	midiOutSetVolume(HMIDIOUT,DWORD);
 UINT		WINAPI	midiOutGetErrorTextA(UINT,LPSTR,UINT);
 UINT		WINAPI	midiOutGetErrorTextW(UINT,LPWSTR,UINT);
 #define 		midiOutGetErrorText WINELIB_NAME_AW(midiOutGetErrorText)
-UINT           WINAPI  midiOutOpen(LPHMIDIOUT,UINT,DWORD_PTR,DWORD_PTR,DWORD);
+MMRESULT        WINAPI  midiOutOpen(LPHMIDIOUT,UINT,DWORD_PTR,DWORD_PTR,DWORD);
 UINT		WINAPI	midiOutClose(HMIDIOUT);
 UINT		WINAPI	midiOutPrepareHeader(HMIDIOUT,MIDIHDR*,UINT);
 UINT		WINAPI	midiOutUnprepareHeader(HMIDIOUT,MIDIHDR*,UINT);
@@ -797,7 +797,7 @@ UINT           WINAPI  midiInGetDevCapsW(UINT_PTR,LPMIDIINCAPSW,UINT);
 UINT		WINAPI	midiInGetErrorTextA(UINT,LPSTR,UINT);
 UINT		WINAPI	midiInGetErrorTextW(UINT,LPWSTR,UINT);
 #define 		midiInGetErrorText WINELIB_NAME_AW(midiInGetErrorText)
-UINT           WINAPI  midiInOpen(LPHMIDIIN,UINT,DWORD_PTR,DWORD_PTR,DWORD);
+MMRESULT        WINAPI  midiInOpen(LPHMIDIIN,UINT,DWORD_PTR,DWORD_PTR,DWORD);
 UINT		WINAPI	midiInClose(HMIDIIN);
 UINT		WINAPI	midiInPrepareHeader(HMIDIIN,MIDIHDR*,UINT);
 UINT		WINAPI	midiInUnprepareHeader(HMIDIIN,MIDIHDR*,UINT);