diff --git a/kitty/config.py b/kitty/config.py
index 51d812cae..b955edeb9 100644
--- a/kitty/config.py
+++ b/kitty/config.py
@@ -104,6 +104,7 @@ def detach_window_parse(func, rest):
 @func_with_args('detach_tab')
 def detach_tab_parse(func, rest):
     if rest not in ('new', 'ask'):
+        log_error('Ignoring invalid detach_tab argument: {}'.format(rest))
         rest = 'new'
     return func, (rest,)