diff --git a/kitty/borders.py b/kitty/borders.py
index f4358b244..440ee1ffa 100644
--- a/kitty/borders.py
+++ b/kitty/borders.py
@@ -26,7 +26,7 @@ def edge(func, os_window_id, tab_id, color, sz, a, b):
 def border(os_window_id, tab_id, color, sz, left, top, right, bottom):
     horz = edge(horizontal_edge, os_window_id, tab_id, color, sz, left, right)
     horz(top), horz(bottom - sz)  # top, bottom edges
-    vert = edge(vertical_edge, color, sz, top, bottom)
+    vert = edge(vertical_edge, os_window_id, tab_id, color, sz, top, bottom)
     vert(left), vert(right - sz)  # left, right edges
 
 
diff --git a/kitty/boss.py b/kitty/boss.py
index bfa4ef17e..ea7cd833c 100644
--- a/kitty/boss.py
+++ b/kitty/boss.py
@@ -70,7 +70,7 @@ class Boss:
         self.opts, self.args = opts, args
         initialize_renderer()
         startup_session = create_session(opts, args)
-        self.add_os_window(startup_session)
+        self.add_os_window(startup_session, os_window_id=os_window_id)
 
     def add_os_window(self, startup_session, os_window_id=None):
         if os_window_id is None: