diff --git a/usr.bin/yacc/main.c b/usr.bin/yacc/main.c
index 96924c18dc33..1533ae7d5229 100644
--- a/usr.bin/yacc/main.c
+++ b/usr.bin/yacc/main.c
@@ -166,7 +166,7 @@ getargs(int argc, char *argv[])
 {
     int ch;
 
-    while ((ch = getopt(argc, argv, "b:dlo:p:rtv")) != -1)
+    while ((ch = getopt(argc, argv, "b:dlo:p:rtvy")) != -1)
     {
 	switch (ch)
 	{
@@ -202,6 +202,10 @@ getargs(int argc, char *argv[])
 	    vflag = 1;
 	    break;
 
+	case 'y':
+	    /* for bison compatibility -- byacc is already POSIX compatible */
+	    break;
+
 	default:
 	    usage();
 	}
diff --git a/usr.bin/yacc/yacc.1 b/usr.bin/yacc/yacc.1
index 56bacbbda7b3..b838872b8f98 100644
--- a/usr.bin/yacc/yacc.1
+++ b/usr.bin/yacc/yacc.1
@@ -44,7 +44,7 @@
 .Nd an LALR(1) parser generator
 .Sh SYNOPSIS
 .Nm
-.Op Fl dlrtv
+.Op Fl dlrtvy
 .Op Fl b Ar file_prefix
 .Op Fl o Ar output_filename
 .Op Fl p Ar symbol_prefix
@@ -118,6 +118,10 @@ so that debugging statements will be incorporated in the compiled code.
 Cause a human-readable description of the generated parser to
 be written to the file
 .Pa y.output .
+.It Fl y
+NOOP for bison compatibility.
+.Nm
+is already designed to be POSIX yacc compatible.
 .El
 .Sh ENVIRONMENT
 .Bl -tag -width ".Ev TMPDIR"