diff --git a/media/capture/video/apple/video_capture_device_avfoundation.mm b/media/capture/video/apple/video_capture_device_avfoundation.mm
index f748a6e570d68..4f1b4d354b521 100644
--- a/media/capture/video/apple/video_capture_device_avfoundation.mm
+++ b/media/capture/video/apple/video_capture_device_avfoundation.mm
@@ -631,7 +631,12 @@ AVCaptureDeviceFormat* FindBestCaptureFormat(
   // `_pendingTakePhotos` just went from 0 to 1. In case the 60 second delayed
   // task to perform stopPhotoOutput() is in-flight, invalidate weak ptrs to
   // cancel any such operation.
-  _weakPtrHolderForTakePhoto.weak_ptr_factory.InvalidateWeakPtrs();
+  // `_lock` is required because captureOutput:didFinishProcessingPhoto:error:
+  // calls GetWeakPtr() on this factory from the AVFoundation delegate queue.
+  {
+    base::AutoLock lock(_lock);
+    _weakPtrHolderForTakePhoto.weak_ptr_factory.InvalidateWeakPtrs();
+  }
 
   // Ready to take a photo immediately?
   // Thread-safe because `_photoOutput` is only modified on the main thread.
@@ -778,10 +783,12 @@ AVCaptureDeviceFormat* FindBestCaptureFormat(
   if (!_photoOutput) {
     return;
   }
-  // Cancel all in-flight operations.
-  _weakPtrHolderForTakePhoto.weak_ptr_factory.InvalidateWeakPtrs();
   {
     base::AutoLock lock(_lock);
+    // Cancel all in-flight operations. `_lock` must be held because
+    // captureOutput:didFinishProcessingPhoto:error: calls GetWeakPtr() on this
+    // factory from the AVFoundation delegate queue while holding `_lock`.
+    _weakPtrHolderForTakePhoto.weak_ptr_factory.InvalidateWeakPtrs();
     if (_captureSession) {
       [_captureSession removeOutput:_photoOutput];
     }