diff --git a/lisp/calendar/appt.el b/lisp/calendar/appt.el
index 68a60a708be..98e555fed13 100644
--- a/lisp/calendar/appt.el
+++ b/lisp/calendar/appt.el
@@ -116,6 +116,9 @@
 
 ;;; Code:
 
+;; Make sure calendar is loaded when we compile this.
+(require 'calendar)
+
 ;;;###autoload
 (defvar appt-issue-message t
   "*Non-nil means check for appointments in the diary buffer.