diff --git a/yasnippet.el b/yasnippet.el
index c225653..86515d8 100644
--- a/yasnippet.el
+++ b/yasnippet.el
@@ -1057,8 +1057,9 @@ name. And under each subdirectory, each file is a definition
 of a snippet. The file name is the trigger key and the
 content of the file is the template."
   (interactive "DSelect the root directory: ")
-  (when (file-directory-p directory)
-    (add-to-list 'yas/root-directory directory))
+  (unless (file-directory-p directory)
+    (error "Error %s not a directory" directory))
+  (add-to-list 'yas/root-directory directory)
   (dolist (dir (yas/directory-files directory nil))
     (yas/load-directory-1 dir))
   (when (interactive-p)