diff --git a/dlls/mfplat/buffer.c b/dlls/mfplat/buffer.c
index 19a7ad33bba..e3f863c6345 100644
--- a/dlls/mfplat/buffer.c
+++ b/dlls/mfplat/buffer.c
@@ -670,13 +670,14 @@ static HRESULT WINAPI d3d9_surface_buffer_Lock2D(IMF2DBuffer2 *iface, BYTE **sca
 
     if (buffer->_2d.linear_buffer)
         hr = MF_E_UNEXPECTED;
-    else if (!buffer->_2d.locks++)
+    else if (!buffer->_2d.locks)
     {
         hr = IDirect3DSurface9_LockRect(buffer->d3d9_surface.surface, &buffer->d3d9_surface.rect, NULL, 0);
     }
 
     if (SUCCEEDED(hr))
     {
+        buffer->_2d.locks++;
         *scanline0 = buffer->d3d9_surface.rect.pBits;
         *pitch = buffer->d3d9_surface.rect.Pitch;
     }
@@ -755,13 +756,14 @@ static HRESULT WINAPI d3d9_surface_buffer_Lock2DSize(IMF2DBuffer2 *iface, MF2DBu
 
     if (buffer->_2d.linear_buffer)
         hr = MF_E_UNEXPECTED;
-    else if (!buffer->_2d.locks++)
+    else if (!buffer->_2d.locks)
     {
         hr = IDirect3DSurface9_LockRect(buffer->d3d9_surface.surface, &buffer->d3d9_surface.rect, NULL, 0);
     }
 
     if (SUCCEEDED(hr))
     {
+        buffer->_2d.locks++;
         *scanline0 = buffer->d3d9_surface.rect.pBits;
         *pitch = buffer->d3d9_surface.rect.Pitch;
         if (buffer_start)