@@ 433,7 433,20 @@ The POST will be skipped
 		   (cond ((stringp content)
 			  (with-temp-buffer
 			    (insert content)
-                            (delete-indentation nil (point-min) (point-max))
+                            ;; XXX: `delete-indentation' holds only 1
+                            ;; argument before 27.x. Create fallback.
+                            (if (version< emacs-version "27")
+                                (let ((prefix (and (> (length fill-prefix) 0)
+                                                   (regexp-quote fill-prefix))))
+                                  (while (and (> (line-beginning-position)
+                                                 (point-min))
+                                              (forward-line 0)
+                                              (= (preceding-char) ?\n))
+                                    (delete-char -1)
+                                    (if (and prefix (looking-at prefix))
+                                        (replace-match "" t t))
+                                    (fixup-whitespace)))
+                              (delete-indentation nil (point-min) (point-max)))
 			    (libxml-parse-html-region (point-min)
 						      (point-max))))
 			 ((consp content)