APC_INDEX_MISMATCH is Windows catching a driver being sloppy with its internal bookkeeping. Drivers are supposed to enter and exit asynchronous procedure calls in matched pairs; when one doesn’t, Windows detects the mismatch and crashes before the inconsistency can cause real damage.

The practical upshot: this is a driver problem about nine times out of ten, and audio drivers are the usual suspects. Here’s how to track it down methodically.

Why this happens

  • Buggy audio driver. Realtek and other audio drivers are the classic cause of this exact stop code.
  • Mismatched driver versions. A driver updated independently of its companion software can fall out of sync.
  • Newly installed hardware. Fresh devices bring fresh drivers, and fresh drivers bring fresh bugs.
  • Corrupted driver installation. An interrupted install leaves a driver in a half-working state.
  • Recent Windows update. Updates change kernel behavior that older drivers depended on.
  • Overclocked system. Unstable overclocks can corrupt the driver state that APC tracking depends on.
  • Virtual machine or sandbox software. Hypervisors and sandboxes install kernel drivers that perform their own asynchronous calls and occasionally get the pairing wrong.

How to fix it

Work through these in order, from Fix 1 onward, and stop as soon as the crashes stop.

Fix 1: Think about what changed recently

Half of APC_INDEX_MISMATCH cases are solved by connecting the crash to a recent change.

  1. Ask yourself: did you plug in new hardware, update a driver, or install new software in the days before the crashes started?
  2. Check Settings > Windows Update > Update history for recent driver updates.
  3. Look at Settings > Apps > Installed apps sorted by install date for new software.
  4. If you identify a suspect, unplug the hardware or uninstall the software as a test before doing anything else.
  5. If the crashes stop, you’ve found it — then decide whether to update that driver or leave the device unplugged.

Fix 2: Update or reinstall the audio driver

Given the history of this stop code, the audio driver deserves first attention.

  1. Press Win + X and open Device Manager.
  2. Expand Sound, video and game controllers.
  3. Right-click your audio device (often Realtek) and choose Update driver > Search automatically for drivers.
  4. If that finds nothing, download the latest audio driver from your laptop maker’s support page — not a generic one.
  5. For a thorough fix, choose Uninstall device (checking Attempt to remove the driver), restart, and then install the fresh download.

Fix 3: Update the display and chipset drivers

After audio, these are the next most likely APC offenders.

  1. In Device Manager, update the display adapter driver.
  2. Install the latest chipset driver package from your laptop maker’s site.
  3. Update any USB controller drivers too — USB audio and docks route through them.
  4. Restart after each major driver change.
  5. Test with audio playing and the usual workload for a day — APC crashes are often triggered by specific activity.

Fix 4: Roll back the suspect driver

If a driver update immediately preceded the crashes, undo it rather than updating further.

  1. In Device Manager, right-click the suspect device and open Properties.
  2. On the Driver tab, click Roll Back Driver and choose a reason.
  3. Restart and test.
  4. If Roll Back is unavailable, uninstall the device (checking Attempt to remove the driver) and let Windows install its built-in version.
  5. Block the bad version from returning via Settings > Windows Update > Advanced options by pausing updates temporarily.

Fix 5: Repair system files

Corrupted system files can make a healthy driver look guilty. Our DISM guide covers the deeper repair.

  1. Open Terminal (Admin) from the Win + X menu.
  2. Run sfc /scannow and wait for it to finish.
  3. Run DISM /Online /Cleanup-Image /RestoreHealth with an internet connection.
  4. Restart the laptop.
  5. Run SFC once more to confirm the second pass is clean.

Fix 6: Remove the recent Windows update

When the crashes align with Patch Tuesday, the update changed something your driver depended on.

  1. Open Settings > Windows Update > Update history > Uninstall updates.
  2. Remove the most recent quality update and restart.
  3. Test for a few days with your normal audio and peripheral use.
  4. If stability returns, pause updates for two weeks to give the driver vendor time to catch up.
  5. Check the driver vendor’s site during the pause — an updated driver often appears within days of a breaking Windows update.

Fix 7: Reset BIOS to defaults and drop overclocks

Unstable overclocks corrupt driver state in ways that surface as APC mismatches.

  1. Restart into the BIOS/UEFI (F2 or Del during boot).
  2. Choose Load Optimized Defaults or Reset to default.
  3. If you use Intel XTU, Ryzen Master, or MSI Afterburner, reset those to stock too.
  4. Save and exit, then test for several days.
  5. Only reintroduce overclocks gradually once you’re confident the crashes are gone.

Fix 8: Use System Restore to go back before the crashes

When you can’t isolate the specific driver, rolling back the whole system state is the pragmatic answer.

  1. Press Win + S, type Create a restore point, and open it.
  2. Click System Restore and choose a point from before the crashes began.
  3. Click Scan for affected programs to see what will be removed.
  4. Complete the wizard and let the restart finish uninterrupted.
  5. Afterward, update drivers one at a time — slowly — so you can identify the bad one if it returns.

Closing

APC_INDEX_MISMATCH is one of the more diagnosable blue screens because the suspect list is short: audio drivers first, then whatever changed recently. Work the list in order and you’ll almost always find it in the first four fixes. Keep a note of which driver version finally proved stable, so a future automatic update doesn’t silently reintroduce the problem. For the same error on specific hardware, see our HP laptop walkthrough , and Microsoft’s official blue screen help covers anything unusual.

Frequently asked questions

What does APC_INDEX_MISMATCH mean?
APC stands for Asynchronous Procedure Call — a mechanism drivers use to schedule work. This stop code means a driver entered and exited these calls inconsistently, leaving the system in a corrupted state. In practice, it almost always points to a buggy or mismatched driver, with audio drivers (especially Realtek) being the most famous repeat offender.
Why does APC_INDEX_MISMATCH often involve audio drivers?
Audio drivers make heavy use of asynchronous calls to keep sound playing smoothly without glitches. Realtek audio drivers in particular have a long history of APC-related bugs across Windows versions. If your crashes mention a file like rtkvhd64.sys or happen when audio starts or stops, the audio driver is almost certainly the culprit.
Can new hardware cause APC_INDEX_MISMATCH?
Yes — newly installed hardware with a buggy or wrong driver is a textbook trigger. USB audio interfaces, webcams, docks, and printers all install drivers that use asynchronous calls. If the crashes started within days of plugging in something new, update that device’s driver first or unplug it temporarily to test.
Does this error damage my files?
No, the blue screen itself doesn’t damage files — it’s Windows stopping to prevent damage. However, the underlying driver bug can theoretically corrupt data if it writes to the wrong place before crashing, which is rare. The standard advice applies: keep backups, but don’t panic about the crashes themselves harming your documents.