diff --git a/docs/changelog.rst b/docs/changelog.rst
index 367862cab..b8fc72276 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -264,6 +264,9 @@ Detailed list of changes
 
 - Cursor trail: Show a cursor trail when switching tabs (:pull:`9588`)
 
+- Make shift+left click extend the current selection instead of starting a new
+  selection when the mouse is not grabbed by the TUI application (:disc:`9608`)
+
 
 0.45.0 [2025-12-24]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/kitty/options/definition.py b/kitty/options/definition.py
index 39b1fdb2b..35845be98 100644
--- a/kitty/options/definition.py
+++ b/kitty/options/definition.py
@@ -983,6 +983,14 @@ boundary, use :code:`move-end` instead of :code:`extend`.
 '''
     )
 
+mma('Extend the current selection with shift',
+    'extend_selection_shift shift+left press ungrabbed mouse_selection extend',
+    long_text='''
+If you want only the end of the selection to be moved instead of the nearest
+boundary, use :code:`move-end` instead of :code:`extend`.
+'''
+    )
+
 mma('Paste from the primary selection even when grabbed',
     'paste_selection_grabbed shift+middle release ungrabbed,grabbed paste_selection',
     )
@@ -992,7 +1000,7 @@ mma('Discard press event for middle click paste',
     )
 
 mma('Start selecting text even when grabbed',
-    'start_simple_selection_grabbed shift+left press ungrabbed,grabbed mouse_selection normal',
+    'start_simple_selection_grabbed shift+left press grabbed mouse_selection normal',
     )
 
 mma('Start selecting text in a rectangle even when grabbed',
diff --git a/kitty/options/types.py b/kitty/options/types.py
index 429a643ed..3502d2fce 100644
--- a/kitty/options/types.py
+++ b/kitty/options/types.py
@@ -1090,6 +1090,8 @@ defaults.mouse_map = [
     MouseMapping(mods=6, repeat_count=3, definition='mouse_selection line_from_point'),
     # extend_selection
     MouseMapping(button=1, definition='mouse_selection extend'),
+    # extend_selection_shift
+    MouseMapping(mods=1, definition='mouse_selection extend'),
     # paste_selection_grabbed
     MouseMapping(button=2, mods=1, repeat_count=-1, grabbed=True, definition='paste_selection'),
     # paste_selection_grabbed
@@ -1098,8 +1100,6 @@ defaults.mouse_map = [
     MouseMapping(button=2, mods=1, grabbed=True, definition='discard_event'),
     # start_simple_selection_grabbed
     MouseMapping(mods=1, grabbed=True, definition='mouse_selection normal'),
-    # start_simple_selection_grabbed
-    MouseMapping(mods=1, definition='mouse_selection normal'),
     # start_rectangle_selection_grabbed
     MouseMapping(mods=7, grabbed=True, definition='mouse_selection rectangle'),
     # start_rectangle_selection_grabbed