D3DX9_42.dll was not found, what it means and how to fix it

D3DX9_42.dll is part of the D3DX9 helper library from the DirectX June 2010 release. Older games built against it need those DirectX 9 era files, which modern Windows does not include, so the error appears on a new PC even though DirectX 12 is installed.

The fix, in order

  1. Install the DirectX End-User Runtime from Microsoft (dxwebsetup.exe). It adds the June 2010 libraries side by side and does not touch DirectX 11 or 12. Restart the PC when done.
  2. Or run the game's own DirectX installer. Look in the game's folder for _CommonRedist/DirectX and run DXSETUP.exe there, which installs exactly the libraries that game expects.
  3. Remove any hand-copied D3DX9_42.dll from the game folder first. A wrong-architecture copy causes the 0xc000007b startup error instead of fixing anything.
  4. Verify the game files. In Steam: right-click → Properties → Installed Files → Verify integrity of game files. A damaged game folder can keep failing next to a healthy runtime.
Do not download D3DX9_42.dll by itself. DLL download sites offer single files of random versions, sometimes bundled with installers nobody asked for. The file belongs to a matched set installed by Microsoft's DirectX End-User Runtime, that package is the fix, and it is free.

If it still happens

If the error names a different D3DX9 file, for example D3DX9_43.dll, the same runtime covers it, since the June 2010 package installs the whole D3DX9 set. If the game still fails, reinstall it cleanly, since a damaged game folder can keep failing next to a healthy runtime.

Common questions

I have DirectX 12, why is a DirectX 9 file missing? The version number only covers the core components. D3DX9 is an optional helper library from the old DirectX SDK, and Windows Update does not provide it. The DirectX End-User Runtime is what adds it.

What if the error names D3DX9_43.dll instead? The same fix covers it. The June 2010 runtime installs the whole D3DX9 set, so one install fixes every numbered D3DX9 file.

Related errors

D3DX9_43.dll missing · Error 0xc000007b · MSVCP140.dll missing

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