diff --git a/ssh-keygen.1 b/ssh-keygen.1
index 3e03a9b..aacd4d3 100644
--- a/ssh-keygen.1
+++ b/ssh-keygen.1
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: ssh-keygen.1,v 1.92 2010/03/13 23:38:13 jmc Exp $
+.\"	$OpenBSD: ssh-keygen.1,v 1.93 2010/04/16 01:47:26 djm Exp $
 .\"
 .\"  -*- nroff -*-
 .\"
@@ -37,7 +37,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: March 13 2010 $
+.Dd $Mdocdate: April 16 2010 $
 .Dt SSH-KEYGEN 1
 .Os
 .Sh NAME
@@ -110,8 +110,9 @@
 .Fl I Ar certificate_identity
 .Op Fl h
 .Op Fl n Ar principals
-.Op Fl O Ar constraint
+.Op Fl O Ar option
 .Op Fl V Ar validity_interval
+.Op Fl z Ar serial_number
 .Ar
 .Nm ssh-keygen
 .Fl L
@@ -299,13 +300,13 @@
 Please see the
 .Sx CERTIFICATES
 section for details.
-.It Fl O Ar constraint
-Specify a certificate constraint when signing a key.
+.It Fl O Ar option
+Specify a certificate option when signing a key.
 This option may be specified multiple times.
 Please see the
 .Sx CERTIFICATES
 section for details.
-The constraints that are valid for user certificates are:
+The options that are valid for user certificates are:
 .Bl -tag -width Ds
 .It Ic clear
 Clear all enabled permissions.
@@ -355,7 +356,7 @@
 format.
 .El
 .Pp
-At present, no constraints are valid for host keys.
+At present, no options are valid for host keys.
 .It Fl P Ar passphrase
 Provides the (old) passphrase.
 .It Fl p
@@ -441,6 +442,10 @@
 .It Fl y
 This option will read a private
 OpenSSH format file and print an OpenSSH public key to stdout.
+.It Fl z Ar serial_number
+Specifies a serial number to be embedded in the certificate to distinguish
+this certificate from others from the same CA.
+The default serial number is zero.
 .El
 .Sh MODULI GENERATION
 .Nm
@@ -501,7 +506,7 @@
 supports signing of keys to produce certificates that may be used for
 user or host authentication.
 Certificates consist of a public key, some identity information, zero or
-more principal (user or host) names and an optional set of constraints that
+more principal (user or host) names and an optional set of options that
 are signed by a Certification Authority (CA) key.
 Clients or servers may then trust only the CA key and verify its signature
 on a certificate rather than trusting many user/host keys.
@@ -541,11 +546,11 @@
 .Dl "$ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub"
 .Pp
 Additional limitations on the validity and use of user certificates may
-be specified through certificate constraints.
-A constrained certificate may disable features of the SSH session, may be
+be specified through certificate options..
+A certificate option may disable features of the SSH session, may be
 valid only when presented from particular source addresses or may
 force the use of a specific command.
-For a list of valid certificate constraints, see the documentation for the
+For a list of valid certificate options, see the documentation for the
 .Fl O
 option above.
 .Pp