Fix: d3dx9_40.dll is missing or not designed to run on Windows

The error “d3dx9_40.dll is missing” is typically encountered when the user tries to open an application or a game that needs this particular DLL (Dynamic Link Library) file.

After cycling to most occurrences that affected users have reported, we concluded that there are two types of error messages associated with the d3dx9_40.dll file:

  • The program can’t start because d3dx9_40.dll is missing from your computer. Try reinstalling the program to fix this problem.
  • C:\Windows\system32\d3dx9_40.dll is either not designed to run on Windows or it contains an error. Try installing the program again using the original installation media or contact your system administrator or the software vendor for support.

Although the two error messages look different, the root cause is often times the same. The vast majority of these errors will occur because the application in question cannot call the d3dx9_40.dll file. This is either because it’s missing from your system or because it’s corrupted.

Most of the time, errors related to the d3dx9_40.dll file are reported in when the user tries to open an older game that uses optional DLL files included in the DirectX 9 distribution.

What is d3dx9_40.dll?

The d3dx9_40.dll file is just a small part of the many DLL files contained in the Microsoft DirectX software distribution packages. Each DLL (Dynamic Link Library) file contains a specific functionality that other 3rd party programs can call upon. This allows multiple programs to share functionalities that are rooted in a single file.

Keep in mind that the d3dx9_40.dll file is part of an optional DirectX 9 update that is not present by default on Windows 8 or Windows 10 (neither does it install via Windows Update).

Warning: Downloading an individual d3dx9_40.dll file from a DLL download site is not advised. Often times, users that took this shortcut found that so-called quick fix actually ended up producing a different error message. Even more, security researchers argue that some of those DLL files that are hosted individually might actually contain malicious code that is designed to leave your system exposed to future virus infections. The best way to resolve an issue of this kind is to only follow those methods that stick to the official channels (such as the ones below).

How to fix errors associated with d3dx9_40.dll

If you’re looking for a viable fix for an error associated with d3dx9_40.dll, start troubleshooting with the methods below. Both methods included below are confirmed to work by users that managed to solve the issue after finding themselves in a similar situation. Please follow the two potential fixes in order until you come upon a method that manages to fix the problem.

Method 1: Installing DirectX End-User Runtimes

Most users that have struggled with an error associated with the d3dx9_40.dll file have managed to promptly address the issue by installing the DirectX End-User Runtimes.

Unless your system is suffering from underlying corruption, the steps below should resolve any issue caused by the d3dx9_40.dll file:

  1. Visit this official Microsoft link (here) and download the installer for DirectX End-User Runtimes.

  2. Once the download is complete, open the installer and follow the on-screen prompts to install the optional DirectX 9 update.
  3. After the installation finishes, reboot your computer and see whether the issue has been resolved by opening the application that was previously displaying the d3dx9_40.dll error.

If you’re still struggling with the same issue, move down to Method 2.

Method 2: Deleting or Renaming the corrupted d3dx9_40.dll

If the first method hasn’t fixed your problem, there’s a strong chance that some corruption is preventing the d3dx9_40.dll file from being replaced with a fresh copy. Luckily, some users facing the same issue discovered a fairly easy workaround.

This method involves deleting the actively used d3dx9_40.dll file from all locations that Windows uses to call upon it. If the corrupted file refuses to be deleted, we’ll rename the DLL file using the .old executable – essentially telling Windows to treat it as an outdated version.

Here’s a quick guide (with screenshots) of removing all the actively used d3dx9_40.dll occurrences and then reinstalling the DirectX redist:

  1. In File Explorer, navigate to C:\ Windows \ System32. In the System 32 folder, either use the search function or scroll to the location of the d3dx9_40.dll manually. Once you find it, right-click on it and choose Delete.
    Note: If deleting it shows a different error, let’s rename it with the .old extension. To do this, right-click on the d3dx9_40.dll file and choose Rename, then simply add the .old termination at the end of the name. This will instruct your operating system to disregard this file, allowing you to install a fresh copy later on.
  2. Once the first location has been dealt with, navigate to C:\ Windows \ SysWOW64 and mirror the same procedure as we did at step 1. After you delete or rename the  d3dx9_40.dll file, you can close File Explorer.
  3. Now let’s fill in the gaps and replace the corrupted  d3dx9_40.dll file with a fresh copy. To do this, visit this link (here), download the DirectX End-User Runtimes, open the installer and follow the on-screen prompts to install it again.
  4. Once the missing DLL file has been installed via the end-user installer, reboot your system. At the next startup, you should be able to open the application without the d3dx9_40.dll error.
Kevin Arrows
Kevin is a dynamic and self-motivated information technology professional, with a Thorough knowledge of all facets pertaining to network infrastructure design, implementation and administration. Superior record of delivering simultaneous large-scale mission critical projects on time and under budget.
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Fix: d3dx9_40.dll is missing or not designed to run on Windows

If the issue is with your Computer or a Laptop you should try using Restoro which can scan the repositories and replace corrupt and missing files. This works in most cases, where the issue is originated due to a system corruption. You can download Restoro by clicking the Download button below.

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