diff --git a/lisp/emacs-lisp/icons.el b/lisp/emacs-lisp/icons.el
index 86c44830308..8ba6d97ea00 100644
--- a/lisp/emacs-lisp/icons.el
+++ b/lisp/emacs-lisp/icons.el
@@ -202,6 +202,10 @@ icons--create
                       (list :height (if (eq height 'line)
                                         (window-default-line-height)
                                       height)))
+                  (if-let ((width (plist-get keywords :width)))
+                      (list :width (if (eq width 'font)
+                                       (default-font-width)
+                                     width)))
                   '(:scale 1)
                   (if-let ((rotation (plist-get keywords :rotation)))
                       (list :rotation rotation))
diff --git a/lisp/outline.el b/lisp/outline.el
index 86ac19aa415..b50f4f81b62 100644
--- a/lisp/outline.el
+++ b/lisp/outline.el
@@ -318,8 +319,14 @@ outline--button-icons
 (defvar-local outline--use-rtl nil
   "Non-nil when direction of clickable buttons is right-to-left.")
 
+(defvar-local outline--margin-width nil
+  "Current margin width.")
+
+(defvar-local outline-margin-width nil
+  "Default margin width.")
+
 (define-icon outline-open nil
-  '((image "outline-open.svg" "outline-open.pbm" :height (0.8 . em))
+  '((image "outline-open.svg" "outline-open.pbm" :width (0.8 . em))
     (emoji "🔽")
     (symbol " ▼ ")
     (text " open "))
@@ -328,7 +335,7 @@ outline-open
   :help-echo "Close this section")
 
 (define-icon outline-close nil
-  '((image "outline-close.svg" "outline-close.pbm" :height (0.8 . em))
+  '((image "outline-close.svg" "outline-close.pbm" :width (0.8 . em))
     (emoji "▶️")
     (symbol " ▶ ")
     (text " close "))
@@ -337,15 +344,14 @@ outline-close
   :help-echo "Open this section")
 
 (define-icon outline-close-rtl outline-close
-  '((image "outline-close.svg" "outline-close.pbm" :height (0.8 . em)
-           :rotation 180)
+  '((image "outline-close.svg" "outline-close.pbm" :width (0.8 . em) :rotation 180)
     (emoji "◀️")
     (symbol " ◀ "))
   "Right-to-left icon used for buttons in closed outline sections."
   :version "29.1")
 
 (define-icon outline-open-in-margins outline-open
-  '((image "outline-open.svg" "outline-open.pbm" :height 10)
+  '((image "outline-open.svg" "outline-open.pbm" :width font)
     (emoji "🔽")
     (symbol "▼")
     (text "v"))
@@ -353,7 +359,7 @@ outline-open-in-margins
   :version "29.1")
 
 (define-icon outline-close-in-margins outline-close
-  '((image "outline-open.svg" "outline-open.pbm" :height 10 :rotation -90)
+  '((image "outline-open.svg" "outline-open.pbm" :width font :rotation -90)
     (emoji "▶️")
     (symbol "▶")
     (text ">"))
@@ -361,7 +367,7 @@ outline-close-in-margins
   :version "29.1")
 
 (define-icon outline-close-rtl-in-margins outline-close-rtl
-  '((image "outline-open.svg" "outline-open.pbm" :height 10 :rotation 90)
+  '((image "outline-open.svg" "outline-open.pbm" :width font :rotation 90)
     (emoji "◀️")
     (symbol "◀")
     (text "<"))
@@ -528,9 +534,22 @@ outline-minor-mode
           (when (and (eq outline-minor-mode-use-buttons 'in-margins)
                      (> 1 (if outline--use-rtl right-margin-width
                             left-margin-width)))
+            (setq outline--margin-width
+                  (or outline-margin-width
+                      (ceiling
+                       (/ (seq-max
+                           (seq-map #'string-pixel-width
+                                    (seq-map #'icon-string
+                                             `(outline-open-in-margins
+                                               ,(if 'outline--use-rtl
+                                                    'outline-close-rtl-in-margins
+                                                  'outline-close-in-margins)))))
+                          (* (default-font-width) 1.0)))))
             (if outline--use-rtl
-                (setq-local right-margin-width (1+ right-margin-width))
-              (setq-local left-margin-width (1+ left-margin-width)))
+                (setq-local right-margin-width (+ right-margin-width
+                                                  outline--margin-width))
+              (setq-local left-margin-width (+ left-margin-width
+                                               outline--margin-width)))
             (setq-local fringes-outside-margins t)
             ;; Force display of margins
             (when (eq (current-buffer) (window-buffer))
@@ -566,8 +587,10 @@ outline-minor-mode
                  (< 0 (if outline--use-rtl right-margin-width
                         left-margin-width)))
         (if outline--use-rtl
-            (setq-local right-margin-width (1- right-margin-width))
-          (setq-local left-margin-width (1- left-margin-width)))
+            (setq-local right-margin-width (- right-margin-width
+                                              outline--margin-width))
+          (setq-local left-margin-width (- left-margin-width
+                                           outline--margin-width)))
         (setq-local fringes-outside-margins nil)
         ;; Force removal of margins
         (when (eq (current-buffer) (window-buffer))