diff --git a/dlls/dmusic/buffer.c b/dlls/dmusic/buffer.c
index 838ceee..0626276 100644
--- a/dlls/dmusic/buffer.c
+++ b/dlls/dmusic/buffer.c
@@ -18,6 +18,8 @@
  */
 
 #include "dmusic_private.h"
+#include "initguid.h"
+#include "dmksctrl.h"
 
 WINE_DEFAULT_DEBUG_CHANNEL(dmusic);
 
@@ -242,7 +244,10 @@
     dmbuffer->IDirectMusicBuffer_iface.lpVtbl = &DirectMusicBuffer_Vtbl;
     dmbuffer->ref = 0; /* Will be inited by QueryInterface */
 
-    memcpy(&dmbuffer->format, &desc->guidBufferFormat, sizeof(GUID));
+    if (IsEqualGUID(&desc->guidBufferFormat, &GUID_NULL))
+        dmbuffer->format = KSDATAFORMAT_SUBTYPE_MIDI;
+    else
+        dmbuffer->format = desc->guidBufferFormat;
     dmbuffer->size = (desc->cbBuffer + 3) & ~3; /* Buffer size must be multiple of 4 bytes */
 
     dmbuffer->data = HeapAlloc(GetProcessHeap(), 0, dmbuffer->size);
diff --git a/dlls/dmusic/tests/dmusic.c b/dlls/dmusic/tests/dmusic.c
index 1e55961..21607cb 100644
--- a/dlls/dmusic/tests/dmusic.c
+++ b/dlls/dmusic/tests/dmusic.c
@@ -130,7 +130,7 @@
 
     hr = IDirectMusicBuffer_GetBufferFormat(dmbuffer, &format);
     ok(hr == S_OK, "IDirectMusicBuffer_GetBufferFormat returned %x\n", hr);
-    todo_wine ok(IsEqualGUID(&format, &KSDATAFORMAT_SUBTYPE_MIDI), "Wrong format returned %s\n", debugstr_guid(&format));
+    ok(IsEqualGUID(&format, &KSDATAFORMAT_SUBTYPE_MIDI), "Wrong format returned %s\n", debugstr_guid(&format));
     hr = IDirectMusicBuffer_GetMaxBytes(dmbuffer, &size);
     ok(hr == S_OK, "IDirectMusicBuffer_GetMaxBytes returned %x\n", hr);
     ok(size == 1024, "Buffer size is %u instead of 1024\n", size);