diff --git a/lisp/org/org-agenda.el b/lisp/org/org-agenda.el
index 91391577f90..965d676c15c 100644
--- a/lisp/org/org-agenda.el
+++ b/lisp/org/org-agenda.el
@@ -49,7 +49,7 @@
 (declare-function calendar-hebrew-date-string   "cal-hebrew" (&optional date))
 (declare-function calendar-islamic-date-string  "cal-islam"  (&optional date))
 (declare-function calendar-iso-date-string      "cal-iso"    (&optional date))
-(declare-function calendar-iso-from-absolute    "cal-iso"    (&optional date))
+(declare-function calendar-iso-from-absolute    "cal-iso"    (date))
 (declare-function calendar-julian-date-string   "cal-julian" (&optional date))
 (declare-function calendar-mayan-date-string    "cal-mayan"  (&optional date))
 (declare-function calendar-persian-date-string  "cal-persia" (&optional date))