diff --git a/dlls/mfplat/buffer.c b/dlls/mfplat/buffer.c
index dd88a661e45..77767c27d94 100644
--- a/dlls/mfplat/buffer.c
+++ b/dlls/mfplat/buffer.c
@@ -1019,9 +1019,34 @@ static HRESULT WINAPI dxgi_surface_buffer_GetScanline0AndPitch(IMF2DBuffer2 *ifa
 static HRESULT WINAPI dxgi_surface_buffer_Lock2DSize(IMF2DBuffer2 *iface, MF2DBuffer_LockFlags flags,
         BYTE **scanline0, LONG *pitch, BYTE **buffer_start, DWORD *buffer_length)
 {
-    FIXME("%p, %#x, %p, %p, %p, %p.\n", iface, flags, scanline0, pitch, buffer_start, buffer_length);
+    struct buffer *buffer = impl_from_IMF2DBuffer2(iface);
+    HRESULT hr = S_OK;
 
-    return E_NOTIMPL;
+    TRACE("%p, %#x, %p, %p, %p, %p.\n", iface, flags, scanline0, pitch, buffer_start, buffer_length);
+
+    if (!scanline0 || !pitch || !buffer_start || !buffer_length)
+        return E_POINTER;
+
+    EnterCriticalSection(&buffer->cs);
+
+    if (buffer->_2d.linear_buffer)
+        hr = MF_E_UNEXPECTED;
+    else if (!buffer->_2d.locks++)
+        hr = dxgi_surface_buffer_map(buffer);
+
+    if (SUCCEEDED(hr))
+    {
+        *scanline0 = buffer->dxgi_surface.map_desc.pData;
+        *pitch = buffer->dxgi_surface.map_desc.RowPitch;
+        if (buffer_start)
+            *buffer_start = *scanline0;
+        if (buffer_length)
+            *buffer_length = buffer->dxgi_surface.map_desc.RowPitch * buffer->_2d.height;
+    }
+
+    LeaveCriticalSection(&buffer->cs);
+
+    return hr;
 }
 
 static HRESULT WINAPI dxgi_buffer_QueryInterface(IMFDXGIBuffer *iface, REFIID riid, void **obj)