diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index f35c84d..f7bd867 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -1083,12 +1083,19 @@ vc-git-region-history-mode
                     (cdr font-lock-defaults))))
 
 
+(defun git--asciify-coding-system ()
+  (unless (let ((samp "Binary files differ"))
+            (string-equal samp (decode-coding-string
+                                samp coding-system-for-read t)))
+    (setq coding-system-for-read 'undecided)))
+
 (autoload 'vc-switches "vc")
 
 (defun vc-git-diff (files &optional rev1 rev2 buffer _async)
   "Get a difference report using Git between two revisions of FILES."
   (let (process-file-side-effects
         (command "diff-tree"))
+    (git--asciify-coding-system)
     (if rev2
         ;; Diffing against the empty tree.
         (unless rev1 (setq rev1 "4b825dc642cb6eb9a060e54bf8d69288fbee4904"))
@@ -1127,6 +1134,7 @@ vc-git-revision-completion-table
     table))
 
 (defun vc-git-annotate-command (file buf &optional rev)
+  (git--asciify-coding-system)
   (let ((name (file-relative-name file)))
     (apply #'vc-git-command buf 'async nil "blame" "--date=short"
 	   (append (vc-switches 'git 'annotate)