diff --git a/lisp/progmodes/grep.el b/lisp/progmodes/grep.el
index 951663e049a..b0105f08ea2 100644
--- a/lisp/progmodes/grep.el
+++ b/lisp/progmodes/grep.el
@@ -1332,7 +1332,7 @@ command before it's run."
 	   (list regexp files dir confirm))))))
   (when (and (stringp regexp) (> (length regexp) 0))
     (unless (and dir (file-accessible-directory-p dir))
-      (setq dir default-directory))
+      (user-error "Unable to open directory: %s" dir))
     (unless (string-equal (file-remote-p dir) (file-remote-p default-directory))
       (let ((default-directory dir))
         (grep-compute-defaults)))
@@ -1437,7 +1437,7 @@ to indicate whether the grep should be case sensitive or not."
     (grep-compute-defaults))
   (when (and (stringp regexp) (> (length regexp) 0))
     (unless (and dir (file-accessible-directory-p dir))
-      (setq dir default-directory))
+      (user-error "Unable to open directory: %s" dir))
     (unless (string-equal (file-remote-p dir) (file-remote-p default-directory))
       (let ((default-directory dir))
         (grep-compute-defaults)))