diff --git a/dlls/midimap/midimap.c b/dlls/midimap/midimap.c
index 0c54d457d54..c7b8da3bff2 100644
--- a/dlls/midimap/midimap.c
+++ b/dlls/midimap/midimap.c
@@ -425,20 +425,25 @@ static DWORD modData(MIDIMAPDATA* mom, DWORD_PTR dwParam)
 static DWORD modPrepare(MIDIMAPDATA* mom, LPMIDIHDR lpMidiHdr, DWORD_PTR dwSize)
 {
     if (MIDIMAP_IsBadData(mom)) return MMSYSERR_ERROR;
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 ||
-	lpMidiHdr->lpData == 0 || (lpMidiHdr->dwFlags & MHDR_INQUEUE))
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
+    if (lpMidiHdr->dwFlags & MHDR_PREPARED)
+	return MMSYSERR_NOERROR;
 
     lpMidiHdr->dwFlags |= MHDR_PREPARED;
-    lpMidiHdr->dwFlags &= ~MHDR_DONE;
+    lpMidiHdr->dwFlags &= ~(MHDR_DONE|MHDR_INQUEUE); /* flags cleared since w2k */
     return MMSYSERR_NOERROR;
 }
 
-static DWORD modUnprepare(MIDIMAPDATA* mom, LPMIDIHDR lpMidiHdr, DWORD_PTR dwParam2)
+static DWORD modUnprepare(MIDIMAPDATA* mom, LPMIDIHDR lpMidiHdr, DWORD_PTR dwSize)
 {
     if (MIDIMAP_IsBadData(mom)) return MMSYSERR_ERROR;
-    if (!(lpMidiHdr->dwFlags & MHDR_PREPARED)) return MIDIERR_UNPREPARED;
-    if (lpMidiHdr->dwFlags & MHDR_INQUEUE) return MIDIERR_STILLPLAYING;
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
+	return MMSYSERR_INVALPARAM;
+    if (!(lpMidiHdr->dwFlags & MHDR_PREPARED))
+	return MMSYSERR_NOERROR;
+    if (lpMidiHdr->dwFlags & MHDR_INQUEUE)
+	return MIDIERR_STILLPLAYING;
 
     lpMidiHdr->dwFlags &= ~MHDR_PREPARED;
     return MMSYSERR_NOERROR;
diff --git a/dlls/winealsa.drv/midi.c b/dlls/winealsa.drv/midi.c
index 279810938a2..ee975e34004 100644
--- a/dlls/winealsa.drv/midi.c
+++ b/dlls/winealsa.drv/midi.c
@@ -565,7 +565,7 @@ static DWORD midClose(WORD wDevID)
  */
 static DWORD midAddBuffer(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
-    TRACE("(%04X, %p, %08X);\n", wDevID, lpMidiHdr, dwSize);
+    TRACE("(%04X, %p, %d);\n", wDevID, lpMidiHdr, dwSize);
 
     if (wDevID >= MIDM_NumDevs) return MMSYSERR_BADDEVICEID;
     if (MidiInDev[wDevID].state == -1) return MIDIERR_NODEVICE;
@@ -600,15 +600,16 @@ static DWORD midAddBuffer(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
  */
 static DWORD midPrepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
-    TRACE("(%04X, %p, %08X);\n", wDevID, lpMidiHdr, dwSize);
+    TRACE("(%04X, %p, %d);\n", wDevID, lpMidiHdr, dwSize);
 
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 ||
-	lpMidiHdr->lpData == 0 || (lpMidiHdr->dwFlags & MHDR_INQUEUE) != 0)
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
+    if (lpMidiHdr->dwFlags & MHDR_PREPARED)
+	return MMSYSERR_NOERROR;
 
     lpMidiHdr->lpNext = 0;
     lpMidiHdr->dwFlags |= MHDR_PREPARED;
-    lpMidiHdr->dwBytesRecorded = 0;
+    lpMidiHdr->dwFlags &= ~(MHDR_DONE|MHDR_INQUEUE); /* flags cleared since w2k */
 
     return MMSYSERR_NOERROR;
 }
@@ -618,17 +619,14 @@ static DWORD midPrepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
  */
 static DWORD midUnprepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
-    TRACE("(%04X, %p, %08X);\n", wDevID, lpMidiHdr, dwSize);
+    TRACE("(%04X, %p, %d);\n", wDevID, lpMidiHdr, dwSize);
 
-    if (wDevID >= MIDM_NumDevs) return MMSYSERR_BADDEVICEID;
-    if (MidiInDev[wDevID].state == -1) return MIDIERR_NODEVICE;
-
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 ||
-	lpMidiHdr->lpData == 0)
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
-
-    if (!(lpMidiHdr->dwFlags & MHDR_PREPARED)) return MIDIERR_UNPREPARED;
-    if (lpMidiHdr->dwFlags & MHDR_INQUEUE) return MIDIERR_STILLPLAYING;
+    if (!(lpMidiHdr->dwFlags & MHDR_PREPARED))
+	return MMSYSERR_NOERROR;
+    if (lpMidiHdr->dwFlags & MHDR_INQUEUE)
+	return MIDIERR_STILLPLAYING;
 
     lpMidiHdr->dwFlags &= ~MHDR_PREPARED;
 
@@ -1024,27 +1022,16 @@ static DWORD modLongData(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
  */
 static DWORD modPrepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
-    TRACE("(%04X, %p, %08X);\n", wDevID, lpMidiHdr, dwSize);
+    TRACE("(%04X, %p, %d);\n", wDevID, lpMidiHdr, dwSize);
 
-    if (midiSeq == NULL) {
-	WARN("can't prepare !\n");
-	return MMSYSERR_NOTENABLED;
-    }
-
-    /* MS doc says that dwFlags must be set to zero, but (kinda funny) MS mciseq drivers
-     * asks to prepare MIDIHDR which dwFlags != 0.
-     * So at least check for the inqueue flag
-     */
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 ||
-	lpMidiHdr->lpData == 0 || (lpMidiHdr->dwFlags & MHDR_INQUEUE) != 0) {
-	WARN("%p %p %08x %d\n", lpMidiHdr, lpMidiHdr ? lpMidiHdr->lpData : NULL,
-             lpMidiHdr ? lpMidiHdr->dwFlags : 0, dwSize);
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
-    }
+    if (lpMidiHdr->dwFlags & MHDR_PREPARED)
+	return MMSYSERR_NOERROR;
 
     lpMidiHdr->lpNext = 0;
     lpMidiHdr->dwFlags |= MHDR_PREPARED;
-    lpMidiHdr->dwFlags &= ~MHDR_DONE;
+    lpMidiHdr->dwFlags &= ~(MHDR_DONE|MHDR_INQUEUE); /* flags cleared since w2k */
     return MMSYSERR_NOERROR;
 }
 
@@ -1053,15 +1040,12 @@ static DWORD modPrepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
  */
 static DWORD modUnprepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
-    TRACE("(%04X, %p, %08X);\n", wDevID, lpMidiHdr, dwSize);
+    TRACE("(%04X, %p, %d);\n", wDevID, lpMidiHdr, dwSize);
 
-    if (midiSeq == NULL) {
-	WARN("can't unprepare !\n");
-	return MMSYSERR_NOTENABLED;
-    }
-
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0)
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
+    if (!(lpMidiHdr->dwFlags & MHDR_PREPARED))
+	return MMSYSERR_NOERROR;
     if (lpMidiHdr->dwFlags & MHDR_INQUEUE)
 	return MIDIERR_STILLPLAYING;
     lpMidiHdr->dwFlags &= ~MHDR_PREPARED;
diff --git a/dlls/winecoreaudio.drv/midi.c b/dlls/winecoreaudio.drv/midi.c
index e84e6dee6b0..491fc7e6dad 100644
--- a/dlls/winecoreaudio.drv/midi.c
+++ b/dlls/winecoreaudio.drv/midi.c
@@ -455,25 +455,14 @@ static DWORD MIDIOut_Prepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
     TRACE("wDevID=%d lpMidiHdr=%p dwSize=%d\n", wDevID, lpMidiHdr, dwSize);
 
-    if (wDevID >= MIDIOut_NumDevs) {
-        WARN("bad device ID : %d\n", wDevID);
-	return MMSYSERR_BADDEVICEID;
-    }
-
-    /* MS doc says that dwFlags must be set to zero, but (kinda funny) MS mciseq drivers
-     * asks to prepare MIDIHDR which dwFlags != 0.
-     * So at least check for the inqueue flag
-     */
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 ||
-	lpMidiHdr->lpData == 0 || (lpMidiHdr->dwFlags & MHDR_INQUEUE) != 0) {
-	WARN("%p %p %08x %lu/%d\n", lpMidiHdr, lpMidiHdr->lpData,
-	           lpMidiHdr->dwFlags, offsetof(MIDIHDR,dwOffset), dwSize);
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
-    }
+    if (lpMidiHdr->dwFlags & MHDR_PREPARED)
+	return MMSYSERR_NOERROR;
 
     lpMidiHdr->lpNext = 0;
     lpMidiHdr->dwFlags |= MHDR_PREPARED;
-    lpMidiHdr->dwFlags &= ~MHDR_DONE;
+    lpMidiHdr->dwFlags &= ~(MHDR_DONE|MHDR_INQUEUE); /* flags cleared since w2k */
     return MMSYSERR_NOERROR;
 }
 
@@ -484,17 +473,14 @@ static DWORD MIDIOut_Unprepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
     TRACE("wDevID=%d lpMidiHdr=%p dwSize=%d\n", wDevID, lpMidiHdr, dwSize);
 
-    if (wDevID >= MIDIOut_NumDevs) {
-        WARN("bad device ID : %d\n", wDevID);
-	return MMSYSERR_BADDEVICEID;
-    }
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0)
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
+    if (!(lpMidiHdr->dwFlags & MHDR_PREPARED))
+	return MMSYSERR_NOERROR;
     if (lpMidiHdr->dwFlags & MHDR_INQUEUE)
 	return MIDIERR_STILLPLAYING;
 
     lpMidiHdr->dwFlags &= ~MHDR_PREPARED;
-
     return MMSYSERR_NOERROR;
 }
 
@@ -707,42 +693,27 @@ static DWORD MIDIIn_Prepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
     TRACE("wDevID=%d lpMidiHdr=%p dwSize=%d\n", wDevID, lpMidiHdr, dwSize);
 
-    if (wDevID >= MIDIIn_NumDevs) {
-        WARN("bad device ID : %d\n", wDevID);
-	return MMSYSERR_BADDEVICEID;
-    }
-    /* MS doc says that dwFlags must be set to zero, but (kinda funny) MS mciseq drivers
-     * asks to prepare MIDIHDR which dwFlags != 0.
-     * So at least check for the inqueue flag
-     */
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 ||
-	lpMidiHdr->lpData == 0 || (lpMidiHdr->dwFlags & MHDR_INQUEUE) != 0) {
-	WARN("Invalid parameter %p %p %08x %d\n", lpMidiHdr, lpMidiHdr->lpData,
-	           lpMidiHdr->dwFlags, dwSize);
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
-    }
+    if (lpMidiHdr->dwFlags & MHDR_PREPARED)
+	return MMSYSERR_NOERROR;
 
     lpMidiHdr->lpNext = 0;
     lpMidiHdr->dwFlags |= MHDR_PREPARED;
-    lpMidiHdr->dwFlags &= ~MHDR_DONE;
+    lpMidiHdr->dwFlags &= ~(MHDR_DONE|MHDR_INQUEUE); /* flags cleared since w2k */
     return MMSYSERR_NOERROR;
 }
 
 static DWORD MIDIIn_Unprepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
     TRACE("wDevID=%d lpMidiHdr=%p dwSize=%d\n", wDevID, lpMidiHdr, dwSize);
-    if (wDevID >= MIDIIn_NumDevs) {
-        WARN("bad device ID : %d\n", wDevID);
-	return MMSYSERR_BADDEVICEID;
-    }
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0) {
-	WARN("Invalid Parameter\n");
+
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
-    }
-    if (lpMidiHdr->dwFlags & MHDR_INQUEUE) {
-	WARN("Still playing\n");
+    if (!(lpMidiHdr->dwFlags & MHDR_PREPARED))
+	return MMSYSERR_NOERROR;
+    if (lpMidiHdr->dwFlags & MHDR_INQUEUE)
 	return MIDIERR_STILLPLAYING;
-    }
 
     lpMidiHdr->dwFlags &= ~MHDR_PREPARED;
     return MMSYSERR_NOERROR;
diff --git a/dlls/wineoss.drv/midi.c b/dlls/wineoss.drv/midi.c
index 1c28a762168..0bf5d879ed1 100644
--- a/dlls/wineoss.drv/midi.c
+++ b/dlls/wineoss.drv/midi.c
@@ -823,7 +823,7 @@ static DWORD midClose(WORD wDevID)
  */
 static DWORD midAddBuffer(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
-    TRACE("(%04X, %p, %08X);\n", wDevID, lpMidiHdr, dwSize);
+    TRACE("(%04X, %p, %d);\n", wDevID, lpMidiHdr, dwSize);
 
     if (wDevID >= MIDM_NumDevs) return MMSYSERR_BADDEVICEID;
     if (MidiInDev[wDevID].state == -1) return MIDIERR_NODEVICE;
@@ -859,15 +859,16 @@ static DWORD midAddBuffer(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
  */
 static DWORD midPrepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
-    TRACE("(%04X, %p, %08X);\n", wDevID, lpMidiHdr, dwSize);
+    TRACE("(%04X, %p, %d);\n", wDevID, lpMidiHdr, dwSize);
 
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 ||
-	lpMidiHdr->lpData == 0 || (lpMidiHdr->dwFlags & MHDR_INQUEUE) != 0)
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
+    if (lpMidiHdr->dwFlags & MHDR_PREPARED)
+	return MMSYSERR_NOERROR;
 
     lpMidiHdr->lpNext = 0;
     lpMidiHdr->dwFlags |= MHDR_PREPARED;
-    lpMidiHdr->dwBytesRecorded = 0;
+    lpMidiHdr->dwFlags &= ~(MHDR_DONE|MHDR_INQUEUE); /* flags cleared since w2k */
 
     return MMSYSERR_NOERROR;
 }
@@ -877,17 +878,14 @@ static DWORD midPrepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
  */
 static DWORD midUnprepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
-    TRACE("(%04X, %p, %08X);\n", wDevID, lpMidiHdr, dwSize);
+    TRACE("(%04X, %p, %d);\n", wDevID, lpMidiHdr, dwSize);
 
-    if (wDevID >= MIDM_NumDevs) return MMSYSERR_BADDEVICEID;
-    if (MidiInDev[wDevID].state == -1) return MIDIERR_NODEVICE;
-
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 ||
-	lpMidiHdr->lpData == 0)
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
-
-    if (!(lpMidiHdr->dwFlags & MHDR_PREPARED)) return MIDIERR_UNPREPARED;
-    if (lpMidiHdr->dwFlags & MHDR_INQUEUE) return MIDIERR_STILLPLAYING;
+    if (!(lpMidiHdr->dwFlags & MHDR_PREPARED))
+	return MMSYSERR_NOERROR;
+    if (lpMidiHdr->dwFlags & MHDR_INQUEUE)
+	return MIDIERR_STILLPLAYING;
 
     lpMidiHdr->dwFlags &= ~MHDR_PREPARED;
 
@@ -920,7 +918,6 @@ static DWORD midReset(WORD wDevID)
     return MMSYSERR_NOERROR;
 }
 
-
 /**************************************************************************
  * 			midStart				[internal]
  */
@@ -1584,27 +1581,16 @@ static DWORD modLongData(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
  */
 static DWORD modPrepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
-    TRACE("(%04X, %p, %08X);\n", wDevID, lpMidiHdr, dwSize);
+    TRACE("(%04X, %p, %d);\n", wDevID, lpMidiHdr, dwSize);
 
-    if (midiSeqFD == -1) {
-	WARN("can't prepare !\n");
-	return MMSYSERR_NOTENABLED;
-    }
-
-    /* MS doc says that dwFlags must be set to zero, but (kinda funny) MS mciseq drivers
-     * asks to prepare MIDIHDR which dwFlags != 0.
-     * So at least check for the inqueue flag
-     */
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 ||
-	lpMidiHdr->lpData == 0 || (lpMidiHdr->dwFlags & MHDR_INQUEUE) != 0) {
-	WARN("%p %p %08x %d\n", lpMidiHdr, lpMidiHdr ? lpMidiHdr->lpData : NULL,
-	           lpMidiHdr ? lpMidiHdr->dwFlags : 0, dwSize);
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
-    }
+    if (lpMidiHdr->dwFlags & MHDR_PREPARED)
+	return MMSYSERR_NOERROR;
 
     lpMidiHdr->lpNext = 0;
     lpMidiHdr->dwFlags |= MHDR_PREPARED;
-    lpMidiHdr->dwFlags &= ~MHDR_DONE;
+    lpMidiHdr->dwFlags &= ~(MHDR_DONE|MHDR_INQUEUE); /* flags cleared since w2k */
     return MMSYSERR_NOERROR;
 }
 
@@ -1613,15 +1599,12 @@ static DWORD modPrepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
  */
 static DWORD modUnprepare(WORD wDevID, LPMIDIHDR lpMidiHdr, DWORD dwSize)
 {
-    TRACE("(%04X, %p, %08X);\n", wDevID, lpMidiHdr, dwSize);
+    TRACE("(%04X, %p, %d);\n", wDevID, lpMidiHdr, dwSize);
 
-    if (midiSeqFD == -1) {
-	WARN("can't unprepare !\n");
-	return MMSYSERR_NOTENABLED;
-    }
-
-    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0)
+    if (dwSize < offsetof(MIDIHDR,dwOffset) || lpMidiHdr == 0 || lpMidiHdr->lpData == 0)
 	return MMSYSERR_INVALPARAM;
+    if (!(lpMidiHdr->dwFlags & MHDR_PREPARED))
+	return MMSYSERR_NOERROR;
     if (lpMidiHdr->dwFlags & MHDR_INQUEUE)
 	return MIDIERR_STILLPLAYING;
     lpMidiHdr->dwFlags &= ~MHDR_PREPARED;
diff --git a/dlls/winmm/tests/midi.c b/dlls/winmm/tests/midi.c
index f02c4f0fd15..65b5e78e643 100644
--- a/dlls/winmm/tests/midi.c
+++ b/dlls/winmm/tests/midi.c
@@ -128,30 +128,79 @@ static void test_midiIn_device(UINT udev, HWND hwnd)
     test_notification(hwnd, "midiInOpen", MIM_OPEN, 0);
 
     memset(&mhdr, 0, sizeof(mhdr));
+    mhdr.dwFlags = MHDR_DONE;
     mhdr.dwUser = 0x56FA552C;
     mhdr.dwBufferLength = 70000; /* > 64KB! */
+    mhdr.dwBytesRecorded = 5;
     mhdr.lpData = HeapAlloc(GetProcessHeap(), 0 , mhdr.dwBufferLength);
     ok(mhdr.lpData!=NULL, "No %d bytes of memory!\n", mhdr.dwBufferLength);
     if (mhdr.lpData) {
         rc = midiInPrepareHeader(hm, &mhdr, offsetof(MIDIHDR,dwOffset)-1);
         ok(rc==MMSYSERR_INVALPARAM, "midiInPrepare tiny rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == MHDR_DONE, "dwFlags=%x\n", mhdr.dwFlags);
+
+        mhdr.dwFlags |= MHDR_INQUEUE;
         rc = midiInPrepareHeader(hm, &mhdr, offsetof(MIDIHDR,dwOffset));
         ok(!rc, "midiInPrepare old size rc=%s\n", mmsys_error(rc));
-        rc = midiInPrepareHeader(hm, &mhdr, sizeof(mhdr));
-        ok(!rc, "midiInPrepare rc=%s\n", mmsys_error(rc));
-        rc = midiInUnprepareHeader(hm, &mhdr, sizeof(mhdr));
-        ok(!rc, "midiInUnprepare rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == (MHDR_PREPARED|MHDR_INQUEUE|MHDR_DONE)/*w9x*/ ||
+           mhdr.dwFlags == MHDR_PREPARED, "dwFlags=%x\n", mhdr.dwFlags);
         trace("MIDIHDR flags=%x when unsent\n", mhdr.dwFlags);
 
-        HeapFree(GetProcessHeap(), 0, mhdr.lpData);
-    }
-    ok(mhdr.dwUser==0x56FA552C, "MIDIHDR.dwUser changed to %lx\n", mhdr.dwUser);
+        mhdr.dwFlags |= MHDR_INQUEUE|MHDR_DONE;
+        rc = midiInPrepareHeader(hm, &mhdr, sizeof(mhdr));
+        ok(!rc, "midiInPrepare rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == (MHDR_PREPARED|MHDR_INQUEUE|MHDR_DONE), "dwFlags=%x\n", mhdr.dwFlags);
 
+        mhdr.dwFlags &= ~MHDR_INQUEUE;
+        rc = midiInUnprepareHeader(hm, &mhdr, sizeof(mhdr));
+        ok(!rc, "midiInUnprepare rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == MHDR_DONE, "dwFlags=%x\n", mhdr.dwFlags);
+
+        mhdr.dwFlags &= ~MHDR_DONE;
+        rc = midiInUnprepareHeader(hm, &mhdr, sizeof(mhdr));
+        ok(!rc, "midiInUnprepare rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == 0, "dwFlags=%x\n", mhdr.dwFlags);
+
+        rc = midiInPrepareHeader(hm, &mhdr, offsetof(MIDIHDR,dwOffset));
+        ok(!rc, "midiInPrepare rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == MHDR_PREPARED, "dwFlags=%x\n", mhdr.dwFlags);
+
+        mhdr.dwFlags |= MHDR_DONE;
+        rc = midiInPrepareHeader(hm, &mhdr, offsetof(MIDIHDR,dwOffset));
+        ok(!rc, "midiInPrepare rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwBytesRecorded == 5, "BytesRec=%u\n", mhdr.dwBytesRecorded);
+
+        mhdr.dwFlags |= MHDR_DONE;
+        rc = midiInAddBuffer(hm, &mhdr, sizeof(mhdr));
+        ok(!rc, "midiAddBuffer rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == (MHDR_PREPARED|MHDR_INQUEUE), "dwFlags=%x\n", mhdr.dwFlags);
+
+        /* w95 does not set dwBytesRecorded=0 within midiInAddBuffer.  Wine does. */
+        if (mhdr.dwBytesRecorded != 0)
+            trace("dwBytesRecorded %u\n", mhdr.dwBytesRecorded);
+
+        rc = midiInAddBuffer(hm, &mhdr, sizeof(mhdr));
+        ok(rc==MIDIERR_STILLPLAYING, "midiAddBuffer rc=%s\n", mmsys_error(rc));
+
+        rc = midiInPrepareHeader(hm, &mhdr, offsetof(MIDIHDR,dwOffset));
+        ok(!rc, "midiInPrepare rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == (MHDR_PREPARED|MHDR_INQUEUE), "dwFlags=%x\n", mhdr.dwFlags);
+    }
     rc = midiInReset(hm); /* Return any pending buffer */
     ok(!rc, "midiInReset rc=%s\n", mmsys_error(rc));
+    test_notification(hwnd, "midiInReset", MIM_LONGDATA, (DWORD_PTR)&mhdr);
+
+    ok(mhdr.dwFlags == (MHDR_PREPARED|MHDR_DONE), "dwFlags=%x\n", mhdr.dwFlags);
+    rc = midiInUnprepareHeader(hm, &mhdr, sizeof(mhdr));
+    ok(!rc, "midiInUnprepare rc=%s\n", mmsys_error(rc));
+
+    ok(mhdr.dwBytesRecorded == 0, "Did some MIDI HW send %u bytes?\n", mhdr.dwBytesRecorded);
 
     rc = midiInClose(hm);
     ok(!rc, "midiInClose rc=%s\n", mmsys_error(rc));
+
+    ok(mhdr.dwUser==0x56FA552C, "MIDIHDR.dwUser changed to %lx\n", mhdr.dwUser);
+    HeapFree(GetProcessHeap(), 0, mhdr.lpData);
     test_notification(hwnd, "midiInClose", MIM_CLOSE, 0);
     test_notification(hwnd, "midiIn over", 0, WHATEVER);
 }
@@ -290,6 +339,7 @@ static void test_midiOut_device(UINT udev, HWND hwnd)
     }
 
     memset(&mhdr, 0, sizeof(mhdr));
+    mhdr.dwFlags = MHDR_DONE;
     mhdr.dwUser   = 0x56FA552C;
     mhdr.dwOffset = 0xDEADBEEF;
     mhdr.dwBufferLength = 70000; /* > 64KB! */
@@ -298,17 +348,41 @@ static void test_midiOut_device(UINT udev, HWND hwnd)
     if (mhdr.lpData) {
         rc = midiOutLongMsg(hm, &mhdr, sizeof(mhdr));
         ok(rc==MIDIERR_UNPREPARED, "midiOutLongMsg unprepared rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == MHDR_DONE, "dwFlags=%x\n", mhdr.dwFlags);
         test_notification(hwnd, "midiOutLong unprepared", 0, WHATEVER);
 
         rc = midiOutPrepareHeader(hm, &mhdr, offsetof(MIDIHDR,dwOffset)-1);
         ok(rc==MMSYSERR_INVALPARAM, "midiOutPrepare tiny rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == MHDR_DONE, "dwFlags=%x\n", mhdr.dwFlags);
+
+        /* Since at least w2k, midiOutPrepare clears the DONE and INQUEUE flags.  w95 didn't. */
+        /* mhdr.dwFlags |= MHDR_INQUEUE; would cause w95 to return STILLPLAYING from Unprepare */
         rc = midiOutPrepareHeader(hm, &mhdr, offsetof(MIDIHDR,dwOffset));
         ok(!rc, "midiOutPrepare old size rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == (MHDR_PREPARED|MHDR_DONE)/*w9x*/ ||
+           mhdr.dwFlags == MHDR_PREPARED, "dwFlags=%x\n", mhdr.dwFlags);
+        trace("MIDIHDR flags=%x when unsent\n", mhdr.dwFlags);
+
+        /* No flag is cleared when already prepared. */
+        mhdr.dwFlags |= MHDR_DONE|MHDR_INQUEUE;
         rc = midiOutPrepareHeader(hm, &mhdr, sizeof(mhdr));
         ok(!rc, "midiOutPrepare rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == (MHDR_PREPARED|MHDR_DONE|MHDR_INQUEUE), "dwFlags=%x\n", mhdr.dwFlags);
+
+        mhdr.dwFlags |= MHDR_INQUEUE;
+        rc = midiOutUnprepareHeader(hm, &mhdr, sizeof(mhdr));
+        ok(rc==MIDIERR_STILLPLAYING, "midiOutUnprepare rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == (MHDR_PREPARED|MHDR_DONE|MHDR_INQUEUE), "dwFlags=%x\n", mhdr.dwFlags);
+
+        mhdr.dwFlags &= ~MHDR_INQUEUE;
         rc = midiOutUnprepareHeader(hm, &mhdr, sizeof(mhdr));
         ok(!rc, "midiOutUnprepare rc=%s\n", mmsys_error(rc));
-        trace("MIDIHDR flags=%x when unsent\n", mhdr.dwFlags);
+        ok(mhdr.dwFlags == MHDR_DONE, "dwFlags=%x\n", mhdr.dwFlags);
+
+        mhdr.dwFlags |= MHDR_INQUEUE;
+        rc = midiOutUnprepareHeader(hm, &mhdr, sizeof(mhdr));
+        ok(!rc, "midiOutUnprepare rc=%s\n", mmsys_error(rc));
+        ok(mhdr.dwFlags == (MHDR_INQUEUE|MHDR_DONE), "dwFlags=%x\n", mhdr.dwFlags);
 
         HeapFree(GetProcessHeap(), 0, mhdr.lpData);
     }
@@ -327,6 +401,7 @@ static void test_midiOut_device(UINT udev, HWND hwnd)
     test_notification(hwnd, "midiOutClose", MOM_CLOSE, 0);
 
     rc = midiOutOpen(&hm, udev, 0, (DWORD_PTR)MYCBINST, CALLBACK_WINDOW);
+    /* w95 broken(rc==MMSYSERR_INVALPARAM) see WINMM_CheckCallback */
     ok(!rc, "midiOutOpen(dev=%d) 0 CALLBACK_WINDOW rc=%s\n", udev, mmsys_error(rc));
     /* PostMessage(hwnd=0) redirects to PostThreadMessage(GetCurrentThreadId())
      * which PeekMessage((HWND)-1) queries. */
diff --git a/dlls/winmm/winmm.c b/dlls/winmm/winmm.c
index aecb9cfe472..bb686e0aa6b 100644
--- a/dlls/winmm/winmm.c
+++ b/dlls/winmm/winmm.c
@@ -476,9 +476,6 @@ UINT WINAPI midiOutPrepareHeader(HMIDIOUT hMidiOut,
 
     TRACE("(%p, %p, %d)\n", hMidiOut, lpMidiOutHdr, uSize);
 
-    if (lpMidiOutHdr == NULL || uSize < offsetof(MIDIHDR,dwOffset))
-	return MMSYSERR_INVALPARAM;
-
     if ((wmld = MMDRV_Get(hMidiOut, MMDRV_MIDIOUT, FALSE)) == NULL)
 	return MMSYSERR_INVALHANDLE;
     /* FIXME: detect MIDIStream handles and enforce 64KB buffer limit on those */
@@ -496,13 +493,6 @@ UINT WINAPI midiOutUnprepareHeader(HMIDIOUT hMidiOut,
 
     TRACE("(%p, %p, %d)\n", hMidiOut, lpMidiOutHdr, uSize);
 
-    if (lpMidiOutHdr == NULL || uSize < offsetof(MIDIHDR,dwOffset))
-	return MMSYSERR_INVALPARAM;
-
-    if (!(lpMidiOutHdr->dwFlags & MHDR_PREPARED)) {
-	return MMSYSERR_NOERROR;
-    }
-
     if ((wmld = MMDRV_Get(hMidiOut, MMDRV_MIDIOUT, FALSE)) == NULL)
 	return MMSYSERR_INVALHANDLE;
 
@@ -592,7 +582,7 @@ UINT WINAPI midiOutCachePatches(HMIDIOUT hMidiOut, UINT uBank,
 				WORD* lpwPatchArray, UINT uFlags)
 {
     /* not really necessary to support this */
-    FIXME("not supported yet\n");
+    FIXME("(%p, %u, %p, %x): Stub\n", hMidiOut, uBank, lpwPatchArray, uFlags);
     return MMSYSERR_NOTSUPPORTED;
 }
 
@@ -602,7 +592,7 @@ UINT WINAPI midiOutCachePatches(HMIDIOUT hMidiOut, UINT uBank,
 UINT WINAPI midiOutCacheDrumPatches(HMIDIOUT hMidiOut, UINT uPatch,
 				    WORD* lpwKeyArray, UINT uFlags)
 {
-    FIXME("not supported yet\n");
+    FIXME("(%p, %u, %p, %x): Stub\n", hMidiOut, uPatch, lpwKeyArray, uFlags);
     return MMSYSERR_NOTSUPPORTED;
 }
 
@@ -774,9 +764,6 @@ UINT WINAPI midiInPrepareHeader(HMIDIIN hMidiIn,
 
     TRACE("(%p, %p, %d)\n", hMidiIn, lpMidiInHdr, uSize);
 
-    if (lpMidiInHdr == NULL || uSize < offsetof(MIDIHDR,dwOffset))
-	return MMSYSERR_INVALPARAM;
-
     if ((wmld = MMDRV_Get(hMidiIn, MMDRV_MIDIIN, FALSE)) == NULL)
 	return MMSYSERR_INVALHANDLE;
 
@@ -793,13 +780,6 @@ UINT WINAPI midiInUnprepareHeader(HMIDIIN hMidiIn,
 
     TRACE("(%p, %p, %d)\n", hMidiIn, lpMidiInHdr, uSize);
 
-    if (lpMidiInHdr == NULL || uSize < offsetof(MIDIHDR,dwOffset))
-	return MMSYSERR_INVALPARAM;
-
-    if (!(lpMidiInHdr->dwFlags & MHDR_PREPARED)) {
-	return MMSYSERR_NOERROR;
-    }
-
     if ((wmld = MMDRV_Get(hMidiIn, MMDRV_MIDIIN, FALSE)) == NULL)
 	return MMSYSERR_INVALHANDLE;