diff --git a/dlls/winmm/mmio.c b/dlls/winmm/mmio.c
index 7b7dbc3bf67..78ad7da3cd7 100644
--- a/dlls/winmm/mmio.c
+++ b/dlls/winmm/mmio.c
@@ -693,6 +693,7 @@ static HMMIO MMIO_Open(LPSTR szFileName, MMIOINFO* refmminfo, DWORD dwOpenFlags,
 
     wm->ioProc->count++;
     wm->info.dwFlags = dwOpenFlags;
+    wm->info.pIOProc = wm->ioProc->pIOProc;
 
     if (dwOpenFlags & MMIO_ALLOCBUF) {
 	refmminfo->wErrorRet = MMIO_SetBuffer(wm, refmminfo->pchBuffer,
diff --git a/dlls/winmm/tests/mmio.c b/dlls/winmm/tests/mmio.c
index b2c54e0b9cd..df4de55324b 100644
--- a/dlls/winmm/tests/mmio.c
+++ b/dlls/winmm/tests/mmio.c
@@ -753,6 +753,7 @@ static void test_mmioOpen_fourcc(void)
     mmioGetInfo(hmmio, &mmio, 0);
     ok(hmmio && mmio.fccIOProc == FOURCC_XYZ, "mmioOpenA error %u, got %4.4s\n",
             mmio.wErrorRet, (LPCSTR)&mmio.fccIOProc);
+    ok(mmio.pIOProc == mmio_test_IOProc, "Unexpected pIOProc %p\n", mmio.pIOProc);
     ok(mmio.adwInfo[1] == 0, "mmioOpenA sent MMIOM_SEEK, got %ld\n",
        mmio.adwInfo[1]);
     ok(mmio.lDiskOffset == 0, "mmioOpenA updated lDiskOffset, got %ld\n",
@@ -765,6 +766,7 @@ static void test_mmioOpen_fourcc(void)
     mmioGetInfo(hmmio, &mmio, 0);
     ok(hmmio && mmio.fccIOProc == FOURCC_XYZ, "mmioOpenA error %u, got %4.4s\n",
             mmio.wErrorRet, (LPCSTR)&mmio.fccIOProc);
+    ok(mmio.pIOProc == mmio_test_IOProc, "Unexpected pIOProc %p\n", mmio.pIOProc);
     ok(mmio.adwInfo[1] == 0, "mmioOpenA sent MMIOM_SEEK, got %ld\n",
        mmio.adwInfo[1]);
     ok(mmio.lDiskOffset == 0, "mmioOpenA updated lDiskOffset, got %ld\n",