diff --git a/src/lib/format.pl b/src/lib/format.pl
index 6962470e..47150a97 100644
--- a/src/lib/format.pl
+++ b/src/lib/format.pl
@@ -73,6 +73,7 @@
 :- module(format, [format_//2,
                    format/2,
                    format/3,
+                   portray_clause_//1,
                    portray_clause/1,
                    portray_clause/2,
                    listing/1