diff --git a/contrib/bison/getargs.c b/contrib/bison/getargs.c
index ee1a03a7ea8b..659bf7c1b46c 100644
--- a/contrib/bison/getargs.c
+++ b/contrib/bison/getargs.c
@@ -31,6 +31,7 @@ int nolinesflag;
 int noparserflag = 0;
 int toknumflag = 0;
 int rawtoknumflag = 0;
+int broken_undeftoken_init;
 char *spec_name_prefix; /* for -p.  */
 char *spec_file_prefix; /* for -b. */
 extern int fixed_outfiles;/* for -y */
@@ -44,6 +45,7 @@ extern void warns PARAMS((char *, char *));	/* main.c */
 
 struct option longopts[] =
 {
+  {"broken-undeftoken-init", 0, &broken_undeftoken_init, 1},
   {"debug", 0, &debugflag, 1},
   {"defines", 0, &definesflag, 1},
   {"file-prefix", 1, 0, 'b'},
diff --git a/contrib/bison/reader.c b/contrib/bison/reader.c
index e67a11891793..2354942014c6 100644
--- a/contrib/bison/reader.c
+++ b/contrib/bison/reader.c
@@ -44,6 +44,7 @@ The entry point is reader().  */
 int rline_allocated;
 
 extern char *program_name;
+extern int broken_undeftoken_init;
 extern int definesflag;
 extern int nolinesflag;
 extern int noparserflag;
@@ -199,7 +200,10 @@ reader (void)
   /* it is always token number 2.  */
   undeftoken = getsym("$undefined.");
   undeftoken->class = STOKEN;
-  undeftoken->user_token_number = 2;
+  /* XXX ``broken_undeftoken_init'' makes Bison 1.28 bug-compatable
+     with Bison 1.25.  FreeBSD depends on this behavior when compiling
+     EGCS-1.1.2's cc1plus.  */
+  undeftoken->user_token_number = broken_undeftoken_init ? 0 : 2;
   /* Read the declaration section.  Copy %{ ... %} groups to ftable and fdefines file.
      Also notice any %token, %left, etc. found there.  */
   if (noparserflag)