diff --git a/src/cal-period.scm b/src/cal-period.scm
index 2d8216b..711927b 100644
--- a/src/cal-period.scm
+++ b/src/cal-period.scm
@@ -225,7 +225,10 @@
    (run-tests
     period
     (test-equal? sort-period-markers
-		 (sort-period-markers '((start (2023 1)) (stop (2022 10)) (start (2022 3))))
+		 (sort-period-markers
+		  `((start ,(make-cal-month 2023 1))
+		    (stop ,(make-cal-month 2022 10))
+		    (start ,(make-cal-month 2022 3))))
 		 '((start (2022 3)) (stop (2022 10)) (start (2023 1))))
     (test-equal? period-markers->cal-periods
 	         (period-markers->cal-periods