diff --git a/dlls/winmm/winemm.h b/dlls/winmm/winemm.h
index ff13bf9afd0..3c3741c18f5 100644
--- a/dlls/winmm/winemm.h
+++ b/dlls/winmm/winemm.h
@@ -267,7 +267,7 @@ MMRESULT        MIDI_StreamOpen(HMIDISTRM* lphMidiStrm, LPUINT lpuDeviceID,
                                 DWORD cMidi, DWORD_PTR dwCallback,
                                 DWORD_PTR dwInstance, DWORD fdwOpen, BOOL bFrom32);
 UINT            WAVE_Open(HANDLE* lphndl, UINT uDeviceID, UINT uType,
-                          const LPWAVEFORMATEX lpFormat, DWORD_PTR dwCallback, 
+                          LPCWAVEFORMATEX lpFormat, DWORD_PTR dwCallback, 
                           DWORD_PTR dwInstance, DWORD dwFlags, BOOL bFrom32);
 
 HMMIO           MMIO_Open(LPSTR szFileName, MMIOINFO* refmminfo,
diff --git a/dlls/winmm/winmm.c b/dlls/winmm/winmm.c
index 0c132063693..69ca68ff433 100644
--- a/dlls/winmm/winmm.c
+++ b/dlls/winmm/winmm.c
@@ -671,7 +671,7 @@ UINT WINAPI mixerSetControlDetails(HMIXEROBJ hmix, LPMIXERCONTROLDETAILS lpmcd,
 /**************************************************************************
  * 				mixerMessage		[WINMM.@]
  */
-UINT WINAPI mixerMessage(HMIXER hmix, UINT uMsg, DWORD_PTR dwParam1, DWORD_PTR dwParam2)
+DWORD WINAPI mixerMessage(HMIXER hmix, UINT uMsg, DWORD_PTR dwParam1, DWORD_PTR dwParam2)
 {
     LPWINE_MLD		wmld;
 
@@ -2491,7 +2491,7 @@ MMRESULT WINAPI midiStreamStop(HMIDISTRM hMidiStrm)
 }
 
 UINT WAVE_Open(HANDLE* lphndl, UINT uDeviceID, UINT uType, 
-               const LPWAVEFORMATEX lpFormat, DWORD_PTR dwCallback, 
+               LPCWAVEFORMATEX lpFormat, DWORD_PTR dwCallback, 
                DWORD_PTR dwInstance, DWORD dwFlags, BOOL bFrom32)
 {
     HANDLE		handle;
@@ -2528,7 +2528,7 @@ UINT WAVE_Open(HANDLE* lphndl, UINT uDeviceID, UINT uType,
     }
 
     wod.hWave = handle;
-    wod.lpFormat = lpFormat;  /* should the struct be copied iso pointer? */
+    wod.lpFormat = (LPWAVEFORMATEX)lpFormat;  /* should the struct be copied iso pointer? */
     wod.dwCallback = dwCallback;
     wod.dwInstance = dwInstance;
     wod.dnDevNode = 0L;
@@ -2674,8 +2674,8 @@ UINT WINAPI waveOutGetErrorTextW(UINT uError, LPWSTR lpText, UINT uSize)
  *			waveOutOpen			[WINMM.@]
  * All the args/structs have the same layout as the win16 equivalents
  */
-UINT WINAPI waveOutOpen(LPHWAVEOUT lphWaveOut, UINT uDeviceID,
-                       const LPWAVEFORMATEX lpFormat, DWORD_PTR dwCallback,
+MMRESULT WINAPI waveOutOpen(LPHWAVEOUT lphWaveOut, UINT uDeviceID,
+                       LPCWAVEFORMATEX lpFormat, DWORD_PTR dwCallback,
                        DWORD_PTR dwInstance, DWORD dwFlags)
 {
     return WAVE_Open((HANDLE*)lphWaveOut, uDeviceID, MMDRV_WAVEOUT, lpFormat,
@@ -3060,8 +3060,8 @@ UINT WINAPI waveInGetErrorTextW(UINT uError, LPWSTR lpText, UINT uSize)
 /**************************************************************************
  * 				waveInOpen			[WINMM.@]
  */
-UINT WINAPI waveInOpen(HWAVEIN* lphWaveIn, UINT uDeviceID,
-		       const LPWAVEFORMATEX lpFormat, DWORD_PTR dwCallback,
+MMRESULT WINAPI waveInOpen(HWAVEIN* lphWaveIn, UINT uDeviceID,
+		       LPCWAVEFORMATEX lpFormat, DWORD_PTR dwCallback,
 		       DWORD_PTR dwInstance, DWORD dwFlags)
 {
     return WAVE_Open((HANDLE*)lphWaveIn, uDeviceID, MMDRV_WAVEIN, lpFormat,
diff --git a/include/dsound.h b/include/dsound.h
index c93f7779e43..aff2c07909a 100644
--- a/include/dsound.h
+++ b/include/dsound.h
@@ -389,11 +389,6 @@ typedef const DSCBCAPS *LPCDSCBCAPS;
 typedef const GUID *LPCGUID;
 #endif
 
-#ifndef _LPCWAVEFORMATEX_DEFINED
-#define _LPCWAVEFORMATEX_DEFINED
-typedef const WAVEFORMATEX *LPCWAVEFORMATEX;
-#endif
-
 typedef LPVOID* LPLPVOID;
 
 typedef BOOL (CALLBACK *LPDSENUMCALLBACKW)(LPGUID,LPCWSTR,LPCWSTR,LPVOID);
diff --git a/include/mmsystem.h b/include/mmsystem.h
index ac8482b3d8b..1565896d558 100644
--- a/include/mmsystem.h
+++ b/include/mmsystem.h
@@ -485,6 +485,7 @@ typedef struct tWAVEFORMATEX {
     WORD	cbSize;
 } WAVEFORMATEX, *LPWAVEFORMATEX, *NPWAVEFORMATEX, *PWAVEFORMATEX;
 #endif
+typedef const WAVEFORMATEX *LPCWAVEFORMATEX;
 
 UINT 		WINAPI 	waveOutGetNumDevs(void);
 UINT           WINAPI  waveOutGetDevCapsA(UINT_PTR,LPWAVEOUTCAPSA,UINT);
@@ -495,7 +496,7 @@ UINT 		WINAPI 	waveOutSetVolume(HWAVEOUT,DWORD);
 UINT 		WINAPI 	waveOutGetErrorTextA(UINT,LPSTR,UINT);
 UINT 		WINAPI 	waveOutGetErrorTextW(UINT,LPWSTR,UINT);
 #define 	    	waveOutGetErrorText WINELIB_NAME_AW(waveOutGetErrorText)
-UINT           WINAPI  waveOutOpen(HWAVEOUT*,UINT,const LPWAVEFORMATEX,DWORD_PTR,DWORD_PTR,DWORD);
+MMRESULT        WINAPI  waveOutOpen(HWAVEOUT*,UINT,LPCWAVEFORMATEX,DWORD_PTR,DWORD_PTR,DWORD);
 UINT 		WINAPI 	waveOutClose(HWAVEOUT);
 UINT 		WINAPI 	waveOutPrepareHeader(HWAVEOUT,WAVEHDR*,UINT);
 UINT 		WINAPI 	waveOutUnprepareHeader(HWAVEOUT,WAVEHDR*,UINT);
@@ -518,7 +519,7 @@ UINT           WINAPI  waveInGetDevCapsW(UINT_PTR,LPWAVEINCAPSW,UINT);
 UINT 		WINAPI 	waveInGetErrorTextA(UINT,LPSTR,UINT);
 UINT 		WINAPI 	waveInGetErrorTextW(UINT,LPWSTR,UINT);
 #define 		waveInGetErrorText WINELIB_NAME_AW(waveInGetErrorText)
-UINT           WINAPI  waveInOpen(HWAVEIN*,UINT,const LPWAVEFORMATEX,DWORD_PTR,DWORD_PTR,DWORD);
+MMRESULT        WINAPI  waveInOpen(HWAVEIN*,UINT,LPCWAVEFORMATEX,DWORD_PTR,DWORD_PTR,DWORD);
 UINT 		WINAPI  waveInClose(HWAVEIN);
 UINT 		WINAPI  waveInPrepareHeader(HWAVEIN,WAVEHDR*,UINT);
 UINT 		WINAPI  waveInUnprepareHeader(HWAVEIN,WAVEHDR*,UINT);
@@ -1485,7 +1486,7 @@ typedef struct {
 UINT		WINAPI	mixerGetNumDevs(void);
 UINT           WINAPI  mixerOpen(LPHMIXER,UINT,DWORD_PTR,DWORD_PTR,DWORD);
 UINT		WINAPI	mixerClose(HMIXER);
-UINT           WINAPI  mixerMessage(HMIXER,UINT,DWORD_PTR,DWORD_PTR);
+DWORD           WINAPI  mixerMessage(HMIXER,UINT,DWORD_PTR,DWORD_PTR);
 UINT           WINAPI  mixerGetDevCapsA(UINT_PTR,LPMIXERCAPSA,UINT);
 UINT           WINAPI  mixerGetDevCapsW(UINT_PTR,LPMIXERCAPSW,UINT);
 #define 		mixerGetDevCaps WINELIB_NAME_AW(mixerGetDevCaps)