From 764b6f1b23f8429620c8595e6ccb1a4cf5faa44e Mon Sep 17 00:00:00 2001
From: Shelley Vohr <shelley.vohr@gmail.com>
Date: Tue, 29 Jun 2021 18:44:21 +0200
Subject: [PATCH] fix: potential crash on macOS app exit

---
 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 d36a5500f5c6e..f54fe660f1c4b 100644
--- a/shell/browser/native_window_mac.mm
+++ b/shell/browser/native_window_mac.mm
@@ -413,7 +413,7 @@ 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])
@@ -1657,7 +1657,10 @@ 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::OverrideNSWindowContentView() {