diff --git a/docs/changelog.rst b/docs/changelog.rst
index bb0b2b134..a89da491d 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -12,6 +12,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 - Tall and Fat layouts: Add a ``mirrored`` option to put the full size window
   on the opposite edge of the screen (:iss:`2654`)
 
+- Add an option :opt:`confirm_on_os_window_close` to ask for confirmation
+  when closing an OS window with multiple kitty windows.
+
 
 0.17.4 [2020-05-09]
 --------------------
diff --git a/kitty/boss.py b/kitty/boss.py
index 827f02bb8..99ef36bf1 100644
--- a/kitty/boss.py
+++ b/kitty/boss.py
@@ -723,8 +723,28 @@ class Boss:
                     text = '\n'.join(parse_uri_list(text))
                 w.paste(text)
 
+    def close_os_window(self) -> None:
+        tm = self.active_tab_manager
+        if tm is not None:
+            self.confirm_os_window_close(tm.os_window_id)
+
     def confirm_os_window_close(self, os_window_id: int) -> None:
-        mark_os_window_for_close(os_window_id)
+        if not self.opts.confirm_os_window_close:
+            mark_os_window_for_close(os_window_id)
+            return
+        tm = self.os_window_map.get(os_window_id)
+        if tm is not None:
+            w = tm.active_window
+            self._run_kitten('ask', ['--type=yesno', '--message', _(
+                'Are you sure you want to close this OS window, it has {}'
+                ' windows running?').format(tm.number_of_windows)],
+                window=w,
+                custom_callback=partial(self.handle_close_os_window_confirmation, os_window_id)
+            )
+
+    def handle_close_os_window_confirmation(self, os_window_id: int, data: Dict[str, Any], *a: Any) -> None:
+        if data['response'] == 'y':
+            mark_os_window_for_close(os_window_id)
 
     def on_os_window_closed(self, os_window_id: int, viewport_width: int, viewport_height: int) -> None:
         self.cached_values['window-size'] = viewport_width, viewport_height
diff --git a/kitty/config_data.py b/kitty/config_data.py
index 3483cfc15..e76094619 100644
--- a/kitty/config_data.py
+++ b/kitty/config_data.py
@@ -778,6 +778,10 @@ this option can be used to keep the margins as small as possible when resizing t
 Note that this does not currently work on Wayland.
 '''))
 
+o('confirm_os_window_close', 0, option_type=positive_int, long_text=_('''
+Ask for confirmation when closing an OS window that has at least this
+number of kitty windows in it. A value of zero disables confirmation.
+'''))
 # }}}
 
 g('tabbar')   # {{{
@@ -1374,8 +1378,7 @@ if is_macos:
 k('close_tab', 'kitty_mod+q', 'close_tab', _('Close tab'))
 if is_macos:
     k('close_tab', 'cmd+w', 'close_tab', _('Close tab'), add_to_docs=False)
-    #  Not yet implemented
-    #  k('close_os_window', 'shift+cmd+w', 'close_os_window', _('Close os window'), add_to_docs=False)
+    k('close_os_window', 'shift+cmd+w', 'close_os_window', _('Close OS window'), add_to_docs=False)
 k('move_tab_forward', 'kitty_mod+.', 'move_tab_forward', _('Move tab forward'))
 k('move_tab_backward', 'kitty_mod+,', 'move_tab_backward', _('Move tab backward'))
 k('set_tab_title', 'kitty_mod+alt+t', 'set_tab_title', _('Set tab title'))
diff --git a/kitty/tabs.py b/kitty/tabs.py
index 32c6ac207..b582c42b9 100644
--- a/kitty/tabs.py
+++ b/kitty/tabs.py
@@ -631,6 +631,14 @@ class TabManager:  # {{{
         if t is not None:
             return t.active_window
 
+    @property
+    def number_of_windows(self) -> int:
+        count = 0
+        for tab in self:
+            for window in tab:
+                count += 1
+        return count
+
     def tab_for_id(self, tab_id: int) -> Optional[Tab]:
         for t in self.tabs:
             if t.id == tab_id: