diff --git a/contrib/bison/bison.1 b/contrib/bison/bison.1
index 6c031ce35c6..9738696e57c 100644
--- a/contrib/bison/bison.1
+++ b/contrib/bison/bison.1
@@ -320,14 +320,21 @@ bison \-y $*
 .ft R
 .sp
 .RE
-.PP
-The long-named options can be introduced with `+' as well as `\-\-',
-for compatibility with previous releases.  Eventually support for `+'
-will be removed, because it is incompatible with the POSIX.2 standard.
 .SH FILES
 /usr/share/misc/bison.simple	simple parser
 .br
 /usr/share/misc/bison.hairy	complicated parser
+.SH "ENVIRONMENT VARIABLES"
+.TP
+.SM BISON_SIMPLE
+If this is set, it specifies the location in which the
+.B bison.simple
+parser can be found.
+.TP
+.SM BISON_HAIRY
+If this is set, it specifies the location in which the
+.B bison.hairy
+parser can be found.
 .SH SEE ALSO
 .IR yacc (1)
 .br