From 250c39809b67022647a77ef0dc996c20665d8a11 Mon Sep 17 00:00:00 2001
From: Shelley Vohr <shelley.vohr@gmail.com>
Date: Wed, 30 Jun 2021 20:12:17 +0200
Subject: [PATCH] fix: potential crash on macOS app exit (#29941)

---
 shell/browser/native_window_mac.mm | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/shell/browser/native_window_mac.mm b/shell/browser/native_window_mac.mm
index 2e19613ded451..6a167de03df63 100644
--- a/shell/browser/native_window_mac.mm
+++ b/shell/browser/native_window_mac.mm
@@ -498,7 +498,7 @@ void ViewDidMoveToSuperview(NSView* self, SEL _cmd) {
   // Use an NSEvent monitor to listen for the wheel event.
   BOOL __block began = NO;
   wheel_event_monitor_ = [NSEvent
-      addLocalMonitorForEventsMatchingMask:NSScrollWheelMask
+      addLocalMonitorForEventsMatchingMask:NSEventMaskScrollWheel
                                    handler:^(NSEvent* event) {
                                      if ([[event window] windowNumber] !=
                                          [window_ windowNumber])
@@ -539,7 +539,10 @@ void ViewDidMoveToSuperview(NSView* self, SEL _cmd) {
   DCHECK(!IsClosed());
   ui::NativeTheme::GetInstanceForNativeUi()->RemoveObserver(this);
   display::Screen::GetScreen()->RemoveObserver(this);
-  [NSEvent removeMonitor:wheel_event_monitor_];
+  if (wheel_event_monitor_) {
+    [NSEvent removeMonitor:wheel_event_monitor_];
+    wheel_event_monitor_ = nil;
+  }
 }
 
 void NativeWindowMac::RedrawTrafficLights() {