diff --git a/magit.el b/magit.el
index 2b1c1e49..d0ce8b26 100644
--- a/magit.el
+++ b/magit.el
@@ -2144,7 +2144,8 @@ in log buffer."
   (or (not (magit-read-rewrite-info))
       (error "Rewrite in progress."))
   (let* ((orig (magit-git-string "rev-parse HEAD"))
-	 (base (magit-git-string "rev-parse %s^" from))
+	 (base (or (car (magit-commit-parents from))
+		   (error "Can't rewrite a commit without a parent, sorry.")))
 	 (pending (magit-git-lines "rev-list %s.." base)))
     (magit-write-rewrite-info `((orig ,orig)
 				(pending ,@(mapcar #'list pending))))