--- magit-diff.el.bkp	2019-10-17 20:29:21.771892709 +0200
+++ magit-diff.el	2019-10-17 20:53:47.927829447 +0200
@@ -509,12 +509,14 @@
   :group 'magit-faces)
 
 (defface magit-diff-hunk-heading
-  '((((class color) (background light))
+  `((((class color) (background light))
      :background "grey80"
-     :foreground "grey30")
+     :foreground "grey30"
+     ,@(unless (version<= emacs-version "27") '(:extend t)))
     (((class color) (background dark))
      :background "grey25"
-     :foreground "grey70"))
+     :foreground "grey70"
+     ,@(unless (version<= emacs-version "27") '(:extend t))))
   "Face for diff hunk headings."
   :group 'magit-faces)