diff --git a/kitty/rc/set_colors.py b/kitty/rc/set_colors.py
index ae689ff6e..2dece5ecd 100644
--- a/kitty/rc/set_colors.py
+++ b/kitty/rc/set_colors.py
@@ -17,7 +17,7 @@ if TYPE_CHECKING:
     from kitty.cli_stub import SetColorsRCOptions as CLIOptions
 
 
-nullable_colors = ('cursor', 'cursor_text_color', 'tab_bar_background', 'tab_bar_margin_color', 'selection_foreground')
+nullable_colors = ('cursor', 'cursor_text_color', 'tab_bar_background', 'tab_bar_margin_color', 'selection_foreground', 'active_border_color')
 
 
 def parse_colors(args: Iterable[str]) -> Dict[str, Optional[int]]: