diff --git a/lib/libc/stdlib/ptsname.3 b/lib/libc/stdlib/ptsname.3
--- a/lib/libc/stdlib/ptsname.3
+++ b/lib/libc/stdlib/ptsname.3
@@ -29,7 +29,7 @@
 .\" NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 .\" SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd October 17, 2020
+.Dd October 14, 2023
 .Dt PTSNAME 3
 .Os
 .Sh NAME
@@ -104,7 +104,7 @@
 for the master device specified with
 .Fa fildes .
 .Sh RETURN VALUES
-.Rv -std grantpt ptsname_r unlockpt
+.Rv -std grantpt unlockpt
 .Pp
 The
 .Fn ptsname
@@ -112,6 +112,19 @@
 of the slave device on success; otherwise a
 .Dv NULL
 pointer is returned.
+.Pp
+The
+.Fn ptsname_r
+function returns the value 0 if successful;
+otherwise a nonzero value is returned and the global variable
+.Va errno
+is set to indicate the error.
+Note:
+.Fn ptsname_r
+was previously documented as returning -1 on error.
+In the future it will be changed to return an error number, for POSIX
+compatibility.
+Therefore, callers should not check for -1.
 .Sh ERRORS
 The
 .Fn grantpt ,