diff --git a/src/prolog/lib/clpz.pl b/src/prolog/lib/clpz.pl
index 458c5d21..f650cd3a 100644
--- a/src/prolog/lib/clpz.pl
+++ b/src/prolog/lib/clpz.pl
@@ -117,6 +117,7 @@
 :- use_module(library(terms)).
 :- use_module(library(error), []).
 :- use_module(library(si)).
+:- use_module(library(freeze)).
 
 % :- use_module(library(types)).