diff --git a/avy-jump.el b/avy-jump.el
index 539b21b..3bc543b 100644
--- a/avy-jump.el
+++ b/avy-jump.el
@@ -38,7 +38,8 @@
   :prefix "avy-")
 
 (defcustom avy-keys '(?a ?s ?d ?f ?g ?h ?j ?k ?l)
-  "Keys for jumping.")
+  "Keys for jumping."
+  :type '(repeat character))
 
 (defcustom avy-background nil
   "When non-nil, a gray background will be added during the selection."