diff --git a/src/prolog/lib/between.pl b/src/prolog/lib/between.pl
index 38d058c8..16c73145 100644
--- a/src/prolog/lib/between.pl
+++ b/src/prolog/lib/between.pl
@@ -8,7 +8,7 @@
 between(Lower, Upper, X) :-
     must_be(integer, Lower),
     must_be(integer, Upper),
-    can_be(integer, X).
+    can_be(integer, X),
     between_(Lower, Upper, X).
 
 between_(Lower, Upper, Lower) :-