diff --git a/embddr/random.scm b/embddr/random.scm
index d16f3be..2ac65c3 100644
--- a/embddr/random.scm
+++ b/embddr/random.scm
@@ -31,7 +31,9 @@
                constrs)))
 ;;;
 ;;; Make constrained random number generator.
-;;; Constraints is list of '(from to weight)
+;;; Constraints is list of '(from to weight), where
+;;; 'from' - inclusive bottom limit, 'to' - exclusive
+;;; top limit or random range.
 ;;;
 (define (constrained-random-generator constrs)
   (let ((constrs (clean-constraints constrs)))