diff --git a/WOPO.COB b/WOPO.COB
index 24f191e..43f3ad0 100644
--- a/WOPO.COB
+++ b/WOPO.COB
@@ -117,7 +117,7 @@
                VALUE "$NUL$".
            03 BF-CODE PIC X(999)
                VALUE "++++++++++(>++++++(>++++<-)<-)>>.<<+++++(>++++(>--
-      -              "--<-)<-)>>-.<+++(>---<-)>.-.$$".
+      -              "--<-)<-)>>-.<+++(>---<-)>.-.$NUL$".
            03 BF-OUTPUT PIC X(999)
                VALUE SPACES.
            03 CYCLE-LIMIT PIC 9(5)