diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index d93be951a3..d6eda2b688 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -1667,6 +1667,41 @@ vc-checkin
    backend
    patch-string))
 
+(declare-function diff-apply-hunk "diff-mode" (&optional reverse))
+
+(defun vc-default-checkin-patch (backend patch-string comment)
+  (with-current-buffer (get-buffer-create " *vc-checkin-patch*")
+    (erase-buffer)
+    (insert patch-string)
+    (diff-mode)
+    (pcase-let ((`(,backend ,files) (diff-vc-deduce-fileset))
+                (root (vc-call-backend backend 'root default-directory))
+                (tmpdir (make-temp-file "vc-checkin-patch" t)))
+      (dolist (f files)
+        (copy-file (expand-file-name f root)
+                   (expand-file-name f tmpdir)))
+      (unwind-protect
+          (let ((default-directory root))
+            (dolist (f files)
+              (with-current-buffer (get-file-buffer f)
+                (vc-revert-file f)
+                (revert-buffer t t t)))
+            (goto-char (point-min))
+            (while (not (eobp))
+              (diff-apply-hunk))
+            (dolist (f files)
+              (with-current-buffer (get-file-buffer f)
+                (save-buffer 0)))
+            (vc-checkin files backend comment))
+        (dolist (f files)
+          (copy-file (expand-file-name f tmpdir)
+                     (expand-file-name f root)
+                     t)
+          (with-current-buffer (get-file-buffer f)
+            (revert-buffer t t t))
+          (delete-directory tmpdir t))
+        (bury-buffer)))))
+
 ;;; Additional entry points for examining version histories
 
 ;; (defun vc-default-diff-tree (backend dir rev1 rev2)