diff --git a/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.h b/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.h
index bc48685b01b03..967b1c4284559 100644
--- a/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.h
+++ b/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.h
@@ -113,6 +113,9 @@ class NativeAppWindowCocoa : public extensions::NativeAppWindow,
   // Called when the window enters fullscreen.
   void WindowDidEnterFullscreen();
 
+  // Called when the window is about exits fullscreen.
+  void WindowWillExitFullscreen();
+
   // Called when the window exits fullscreen.
   void WindowDidExitFullscreen();
 
diff --git a/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.mm b/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.mm
index dc6bd0c023b7b..a2097a2b59957 100644
--- a/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.mm
+++ b/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.mm
@@ -159,6 +159,11 @@ - (void)windowDidEnterFullScreen:(NSNotification*)notification {
     appWindow_->WindowDidEnterFullscreen();
 }
 
+- (void)windowWillExitFullScreen:(NSNotification*)notification {
+  if (appWindow_)
+    appWindow_->WindowWillExitFullscreen();
+}
+
 - (void)windowDidExitFullScreen:(NSNotification*)notification {
   if (appWindow_)
     appWindow_->WindowDidExitFullscreen();
@@ -825,6 +830,26 @@ - (void)setMouseDownCanMoveWindow:(BOOL)can_move;
   is_maximized_ = false;
   is_fullscreen_ = true;
   app_window_->OnNativeWindowChanged();
+
+  // #5651: show system buttons when entered fullscreen
+  if (!has_frame_) {
+    [[window() standardWindowButton:NSWindowZoomButton] setHidden:NO];
+    [[window() standardWindowButton:NSWindowMiniaturizeButton] setHidden:NO];
+    [[window() standardWindowButton:NSWindowCloseButton] setHidden:NO];
+    [[window() standardWindowButton:NSWindowZoomButton] setEnabled:YES];
+  }
+}
+
+void NativeAppWindowCocoa::WindowWillExitFullscreen() {
+  // #5651: and hide these buttons when about to exit fullscreen
+  // If doing this in WindowDidExitFullscreen, users will see the buttons
+  // disappear after restored to normal.
+  if (!has_frame_) {
+    [[window() standardWindowButton:NSWindowZoomButton] setHidden:YES];
+    [[window() standardWindowButton:NSWindowMiniaturizeButton] setHidden:YES];
+    [[window() standardWindowButton:NSWindowCloseButton] setHidden:YES];
+    [[window() standardWindowButton:NSWindowZoomButton] setEnabled:NO];
+  }
 }
 
 void NativeAppWindowCocoa::WindowDidExitFullscreen() {