diff --git a/brmsaptool.scm b/brmsaptool.scm
index 1b10341..a31e19a 100644
--- a/brmsaptool.scm
+++ b/brmsaptool.scm
@@ -218,6 +218,25 @@
   (unit-test 'month-diff (= (month-diff '(2023 1) '(2022 2)) -11))
   (print " ok."))
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Periods
+
+(define (sort-period-markers l)
+  l)
+
+(define (period-markers->periods l)
+  l)
+
+(define (period-duration p)
+  1)
+
+(define (periods-duration l)
+  1)
+
+(define (period-tests!)
+  (display "[test] period ")
+  (print " ok."))
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Members database
 
@@ -323,6 +342,7 @@
 (print "Running self-tests:")
 (dict-tests!)
 (month-tests!)
+(period-tests!)
 (print "All self-tests ok!")
 (newline)