diff --git a/ui/views/win/hwnd_message_handler.cc b/ui/views/win/hwnd_message_handler.cc
index e00c2c13c1803..1fd49ff95c4b1 100644
--- a/ui/views/win/hwnd_message_handler.cc
+++ b/ui/views/win/hwnd_message_handler.cc
@@ -439,6 +439,12 @@ HWNDMessageHandler::~HWNDMessageHandler() {
   // Unhook MoveLoopMouseWatcher, to prevent call backs to this after deletion.
   MoveLoopMouseWatcher::UnhookForHost(this);
 
+  // Defense in depth: ensure no reference to `this` survives in the static
+  // fullscreen monitor map. OnDestroy() already calls this, but the map can
+  // hold duplicate entries if the window migrated monitors while fullscreen,
+  // and OnDestroy() may not run on every destruction path.
+  RemoveCurrentWindowFromFullscreenMonitorMap();
+
   // Clear pointer to this in `hwnd()`'s user data, to prevent installed hooks
   // from calling back into this after deletion.
   ClearUserData();
@@ -3891,12 +3897,16 @@ POINT HWNDMessageHandler::GetCursorPos() const {
 }
 
 void HWNDMessageHandler::RemoveCurrentWindowFromFullscreenMonitorMap() {
-  auto& map = fullscreen_monitor_map_.Get();
-  const auto i = std::ranges::find(
-      map, this, &FullscreenWindowMonitorMap::value_type::second);
-  if (i != map.end()) {
-    map.erase(i);
-  }
+  // Erase *every* entry whose value is `this`. The map can transiently hold
+  // more than one entry for the same handler if the fullscreen window was
+  // migrated to a different monitor outside of SetFullscreen() (e.g. via
+  // Win+Shift+Arrow or after a monitor hot-unplug), because SetFullscreen()
+  // erases by current-monitor key rather than by value. Erasing only the
+  // first match would leave a dangling pointer in the static map after
+  // destruction, which CheckAndHandleBackgroundFullscreenOnMonitor() would
+  // later dereference.
+  std::erase_if(fullscreen_monitor_map_.Get(),
+                [this](const auto& kv) { return kv.second == this; });
 }
 
 void HWNDMessageHandler::UpdateFullscreenMonitorMap() {