diff --git a/etc/images/outline-close.pbm b/etc/images/outline-close.pbm
new file mode 100644
index 00000000000..b37b640b555
Binary files /dev/null and b/etc/images/outline-close.pbm differ
diff --git a/etc/images/outline-open.pbm b/etc/images/outline-open.pbm
new file mode 100644
index 00000000000..06b520f14c9
Binary files /dev/null and b/etc/images/outline-open.pbm differ
diff --git a/lisp/outline.el b/lisp/outline.el
index aee6f696b5b..25f3b21e632 100644
--- a/lisp/outline.el
+++ b/lisp/outline.el
@@ -294,6 +294,7 @@ buffers (yet) -- that will be amended in a future version."
 
 (define-icon outline-open nil
   '((image "outline-open.svg" :height 15 :ascent center)
+    (image "outline-open.pbm" :height 15 :ascent center)
     (emoji "🔽")
     (symbol " ▼ ")
     (text " open "))
@@ -303,6 +304,7 @@ buffers (yet) -- that will be amended in a future version."
 
 (define-icon outline-close nil
   '((image "outline-close.svg" :height 15 :ascent center)
+    (image "outline-close.pbm" :height 15 :ascent center)
     (emoji "▶️")
     (symbol " ▶ ")
     (text " close "))