Index: lib/libc/stdlib/ptsname.3
===================================================================
--- lib/libc/stdlib/ptsname.3
+++ lib/libc/stdlib/ptsname.3
@@ -104,7 +104,20 @@
 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_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.
 .Pp
 The
 .Fn ptsname