diff -Nur mpb-1.4.2.orig/mpb-ctl/field-smob.c mpb-1.4.2/mpb-ctl/field-smob.c
--- mpb-1.4.2.orig/mpb-ctl/field-smob.c	2012-08-07 20:56:24.538452994 -0700
+++ mpb-1.4.2/mpb-ctl/field-smob.c	2012-08-07 20:56:43.713557380 -0700
@@ -157,7 +157,7 @@
 boolean cur_fieldp(SCM obj)
 {
      if (SCM_NIMP(obj) && SCM_SYMBOLP(obj)) {
-	  char *s = gh_symbol2newstr(obj, NULL);
+	  char *s = gh_symbol2newstr(obj);
 	  int ret = !strcmp(s, "cur-field");
 	  free(s);
 	  return ret;