diff --git a/shell/browser/native_window.cc b/shell/browser/native_window.cc
index 90540c2689..07d374226c 100644
--- a/shell/browser/native_window.cc
+++ b/shell/browser/native_window.cc
@@ -537,7 +537,7 @@ void NativeWindow::PreviewFile(const std::string& path,
 
 void NativeWindow::CloseFilePreview() {}
 
-gfx::Rect NativeWindow::GetWindowControlsOverlayRect() {
+absl::optional<gfx::Rect> NativeWindow::GetWindowControlsOverlayRect() {
   return overlay_rect_;
 }
 
@@ -665,6 +665,7 @@ void NativeWindow::NotifyWindowMoved() {
 }
 
 void NativeWindow::NotifyWindowEnterFullScreen() {
+  NotifyLayoutWindowControlsOverlay();
   for (NativeWindowObserver& observer : observers_)
     observer.OnWindowEnterFullScreen();
 }
@@ -690,6 +691,7 @@ void NativeWindow::NotifyWindowSheetEnd() {
 }
 
 void NativeWindow::NotifyWindowLeaveFullScreen() {
+  NotifyLayoutWindowControlsOverlay();
   for (NativeWindowObserver& observer : observers_)
     observer.OnWindowLeaveFullScreen();
 }
@@ -733,10 +735,10 @@ void NativeWindow::NotifyWindowSystemContextMenu(int x,
 }
 
 void NativeWindow::NotifyLayoutWindowControlsOverlay() {
-  gfx::Rect bounding_rect = GetWindowControlsOverlayRect();
-  if (!bounding_rect.IsEmpty()) {
+  auto bounding_rect = GetWindowControlsOverlayRect();
+  if (bounding_rect.has_value()) {
     for (NativeWindowObserver& observer : observers_)
-      observer.UpdateWindowControlsOverlay(bounding_rect);
+      observer.UpdateWindowControlsOverlay(bounding_rect.value());
   }
 }
 
diff --git a/shell/browser/native_window.h b/shell/browser/native_window.h
index 79bc09f9c8..6abcb44fa7 100644
--- a/shell/browser/native_window.h
+++ b/shell/browser/native_window.h
@@ -286,7 +286,7 @@ class NativeWindow : public base::SupportsUserData,
     return weak_factory_.GetWeakPtr();
   }
 
-  virtual gfx::Rect GetWindowControlsOverlayRect();
+  virtual absl::optional<gfx::Rect> GetWindowControlsOverlayRect();
   virtual void SetWindowControlsOverlayRect(const gfx::Rect& overlay_rect);
 
   // Methods called by the WebContents.
diff --git a/shell/browser/native_window_mac.h b/shell/browser/native_window_mac.h
index 95a164bafa..6ce521b5e9 100644
--- a/shell/browser/native_window_mac.h
+++ b/shell/browser/native_window_mac.h
@@ -153,7 +153,7 @@ class NativeWindowMac : public NativeWindow,
   void CloseFilePreview() override;
   gfx::Rect ContentBoundsToWindowBounds(const gfx::Rect& bounds) const override;
   gfx::Rect WindowBoundsToContentBounds(const gfx::Rect& bounds) const override;
-  gfx::Rect GetWindowControlsOverlayRect() override;
+  absl::optional<gfx::Rect> GetWindowControlsOverlayRect() override;
   void NotifyWindowEnterFullScreen() override;
   void NotifyWindowLeaveFullScreen() override;
   void SetActive(bool is_key) override;
diff --git a/shell/browser/native_window_mac.mm b/shell/browser/native_window_mac.mm
index e0ff57736c..5bc222a127 100644
--- a/shell/browser/native_window_mac.mm
+++ b/shell/browser/native_window_mac.mm
@@ -1899,23 +1899,33 @@ void NativeWindowMac::SetForwardMouseMessages(bool forward) {
   [window_ setAcceptsMouseMovedEvents:forward];
 }
 
-gfx::Rect NativeWindowMac::GetWindowControlsOverlayRect() {
-  if (titlebar_overlay_ && buttons_proxy_ &&
-      window_button_visibility_.value_or(true)) {
+absl::optional<gfx::Rect> NativeWindowMac::GetWindowControlsOverlayRect() {
+  if (!titlebar_overlay_)
+    return absl::nullopt;
+
+  // On macOS, when in fullscreen mode, window controls (the menu bar, title
+  // bar, and toolbar) are attached to a separate NSView that slides down from
+  // the top of the screen, independent of, and overlapping the WebContents.
+  // Disable WCO when in fullscreen, because this space is inaccessible to
+  // WebContents. https://crbug.com/915110.
+  if (IsFullscreen())
+    return gfx::Rect();
+
+  if (buttons_proxy_ && window_button_visibility_.value_or(true)) {
     NSRect buttons = [buttons_proxy_ getButtonsContainerBounds];
     gfx::Rect overlay;
     overlay.set_width(GetContentSize().width() - NSWidth(buttons));
-    if ([buttons_proxy_ useCustomHeight]) {
-      overlay.set_height(titlebar_overlay_height());
-    } else {
-      overlay.set_height(NSHeight(buttons));
-    }
+    overlay.set_height([buttons_proxy_ useCustomHeight]
+                           ? titlebar_overlay_height()
+                           : NSHeight(buttons));
 
     if (!base::i18n::IsRTL())
       overlay.set_x(NSMaxX(buttons));
+
     return overlay;
   }
-  return gfx::Rect();
+
+  return absl::nullopt;
 }
 
 // static