So as far as I understand all that's needed to build Wine with the new Windows-on-Windows support is to do: ./configure --enable-archs=i386,x86_64 make But then when I run WineTest I get 60+ failures instead of the usual ~16 on my machine. https://test.winehq.org/queue/err5z_5H/report https://test.winehq.org/queue/errloGNj/report That does not entirely surprise me since this mode has never been tested (neither GitLab nor the TestBot support it). But did I miss something? For instance one failure I get is with devenum:devenum: devenum:devenum start dlls/devenum/tests/devenum.c devenum.c:691: Test failed: Got hr 0x80004005. Unhandled exception: page fault on read access to 0x00000000 in 32-bit code (0x00405a75). The reason for the crash is that wg_transform_create() in main.c returns NULL: if (WINE_UNIX_CALL(unix_wg_transform_create, &params)) return NULL; // <---- we return NULL here without actually calling the implementation in wg_transform.c as far as I can see. Here's the list of test units that fail in one of the runs. Lots of Direct3D (but not all) and multimedia (GStreamer?) tests. Maybe there are some quick gains to be had? (then there's msvcrt:file which gets -2 as a file descriptor) advapi32:security amstream:amstream comctl32:subclass d2d1:d2d1 d3d10core:d3d10core d3d11:d3d11 d3d8:visual d3d9:visual d3dcompiler_43:hlsl_d3d11 d3dcompiler_43:hlsl_d3d9 d3dcompiler_46:hlsl_d3d11 d3dcompiler_46:hlsl_d3d9 d3dcompiler_47:hlsl_d3d11 d3dcompiler_47:hlsl_d3d9 d3dx10_34:d3dx10 d3dx10_35:d3dx10 d3dx10_36:d3dx10 d3dx10_37:d3dx10 d3dx10_38:d3dx10 d3dx10_39:d3dx10 d3dx10_40:d3dx10 d3dx10_41:d3dx10 d3dx10_42:d3dx10 d3dx10_43:d3dx10 d3dx9_36:core d3dx9_36:math d3dx9_36:texture d3dx9_36:volume dbghelp:dbghelp ddraw:d3d ddraw:visual devenum:devenum explorer.exe:explorer gdi32:font iphlpapi:iphlpapi kernel32:debugger kernel32:thread kernel32:virtual mfmediaengine:mfmediaengine mfplay:mfplay mf:mf mf:transform msvcrt:file msvfw32:mciwnd ntdll:info ntdll:virtual ntdll:wow64 opengl32:opengl qasf:asfreader qedit:mediadet quartz:filtergraph quartz:vmr7 quartz:vmr9 riched20:editor user32:class user32:clipboard user32:msg user32:win win32u:win32u wininet:internet winmm:mci wmp:media wmvcore:wmvcore -- Francois Gouget &lt;fgouget(a)codeweavers.com&gt;