diff --git a/lisp/outline.el b/lisp/outline.el
index 1ff0a5a34e5..2a6f475a0db 100644
--- a/lisp/outline.el
+++ b/lisp/outline.el
@@ -35,6 +35,8 @@
 
 ;;; Code:
 
+(eval-when-compile (require 'cl-lib))
+
 (defgroup outlines nil
   "Support for hierarchical outlining."
   :prefix "outline-"