diff --git a/src/cal-period.scm b/src/cal-period.scm
index eb5dd7e..3fa1dd4 100644
--- a/src/cal-period.scm
+++ b/src/cal-period.scm
@@ -186,10 +186,12 @@
  (define (cal-month-in-period? p . ml)
    (let ((m (if (null? ml)
 		(*current-month*)
-		(car ml))))
-     (and (or (not (cal-period-before p))
-	      (cal-month<? m (cal-period-before p)))
-	  (not (cal-month<? m (cal-period-since p))))))
+		(car ml)))
+	 (before (cal-ensure-month (cal-period-before p) #t))
+	 (since (cal-ensure-month (cal-period-since p))))
+     (and (or (not before)
+	      (cal-month<? m before))
+	  (not (cal-month<? m since)))))
 
  ;; Returns true if given month is in at least one of the periods
  ;; given. Defaults to current month.
@@ -234,12 +236,13 @@
 	      (prev #f))
      (if (null? lst)
 	 (reverse
-	  (cons (cons (make-cal-period (car prev) #f)
+	  (cons (cons (make-cal-period (apply make-cal-month (car prev)) #f)
 		      (cdr prev))
 		res))
 	 (loop (cdr lst)
 	       (if prev
-		   (cons (cons (make-cal-period (car prev) (caar lst))
+		   (cons (cons (make-cal-period (apply make-cal-month (car prev))
+						(apply make-cal-month (caar lst)))
 			       (cdr prev))
 			 res)
 		   res)
@@ -256,9 +259,11 @@
 
  ;; Wrapper that accepts either day or month and returns testable month
  (define (cal-ensure-month v . stop?s)
-   (if (cal-month? v)
-       v
-       (apply cal-day->month v stop?s)))
+   (if v
+       (if (cal-month? v)
+	   v
+	   (apply cal-day->month v stop?s))
+       #f))
 
  ;; Performs self-tests of the period module.
  (define (cal-period-tests!)