diff --git a/kitty/layout/splits.py b/kitty/layout/splits.py
index ba6949546..0aad98603 100644
--- a/kitty/layout/splits.py
+++ b/kitty/layout/splits.py
@@ -515,9 +515,7 @@ def add_non_overlay_window(
         aw = next_to or all_windows.active_window
         if bias:
             bias = max(0, min(abs(bias), 100)) / 100
-        if aw is not None:
-            ag = all_windows.active_group
-            assert ag is not None
+        if aw is not None and (ag := all_windows.group_for_window(aw)) is not None:
             group_id = ag.id
             pair = self.pairs_root.pair_for_window(group_id)
             if pair is not None: