diff --git a/docs/changelog.rst b/docs/changelog.rst
index 87893624e..aac698a98 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -181,6 +181,9 @@ Detailed list of changes
 
 - Add support for Unicode 17
 
+- Fix a regression in 0.43.0 that caused :opt:`tab_bar_margin_width` to be
+  doubled on the right edge of the tab bar (:iss:`9154`)
+
 0.43.1 [2025-10-01]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/kitty/tab_bar.py b/kitty/tab_bar.py
index 65def55c8..07ced098b 100644
--- a/kitty/tab_bar.py
+++ b/kitty/tab_bar.py
@@ -697,14 +697,17 @@ class TabBar:
             return
         self.cell_width = cell_width
         s = self.screen
-        viewport_width = max(4 * cell_width, tab_bar.width - 2 * self.margin_width)
-        ncells = viewport_width // cell_width
+        available_width = tab_bar.width - 2 * self.margin_width
+        ncells = max(4, available_width // cell_width)
         s.resize(1, ncells)
         s.reset_mode(DECAWM)
+        cell_area_width = ncells * cell_width
+        available_width_for_left_margin = max(0, tab_bar.width - self.margin_width - cell_area_width)
+        extra_width = max(0, tab_bar.width - 2 * self.margin_width - cell_area_width)
+        left_margin = min(self.margin_width + extra_width // 2, available_width_for_left_margin)
         self.laid_out_once = True
-        margin = (viewport_width - ncells * cell_width) // 2 + self.margin_width
         self.window_geometry = g = WindowGeometry(
-            margin, tab_bar.top, viewport_width - margin, tab_bar.bottom, s.columns, s.lines)
+            left_margin, tab_bar.top, left_margin + cell_area_width, tab_bar.bottom, s.columns, s.lines)
         self.update_blank_rects(central, tab_bar, vw, vh)
         set_tab_bar_render_data(self.os_window_id, self.screen, *g[:4])