diff --git a/lib/libc/stdtime/ctime.3 b/lib/libc/stdtime/ctime.3
index 698a63cfa73d..96b7f775535a 100644
--- a/lib/libc/stdtime/ctime.3
+++ b/lib/libc/stdtime/ctime.3
@@ -1,388 +1,402 @@
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 .\" Arthur Olson.
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 .\"    notice, this list of conditions and the following disclaimer.
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 .\"
 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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 .\"
-.Dd April 20, 2023
+.Dd March 26, 2024
 .Dt CTIME 3
 .Os
 .Sh NAME
 .Nm asctime ,
 .Nm asctime_r ,
 .Nm ctime ,
 .Nm ctime_r ,
 .Nm difftime ,
 .Nm gmtime ,
 .Nm gmtime_r ,
 .Nm localtime ,
 .Nm localtime_r ,
 .Nm mktime ,
 .Nm timegm
 .Nd transform binary date and time values
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
 .In time.h
 .Vt extern char *tzname[2] ;
 .Ft char *
 .Fn asctime "const struct tm *tm"
 .Ft char *
 .Fn asctime_r "const struct tm *tm" "char *buf"
 .Ft char *
 .Fn ctime "const time_t *clock"
 .Ft char *
 .Fn ctime_r "const time_t *clock" "char *buf"
 .Ft double
 .Fn difftime "time_t time1" "time_t time0"
 .Ft struct tm *
 .Fn gmtime "const time_t *clock"
 .Ft struct tm *
 .Fn gmtime_r "const time_t *clock" "struct tm *result"
 .Ft struct tm *
 .Fn localtime "const time_t *clock"
 .Ft struct tm *
 .Fn localtime_r "const time_t *clock" "struct tm *result"
 .Ft time_t
 .Fn mktime "struct tm *tm"
 .Ft time_t
 .Fn timegm "struct tm *tm"
 .Sh DESCRIPTION
 The
 .Fn ctime ,
 .Fn gmtime ,
 and
 .Fn localtime
 functions all take as argument a pointer to a time value representing
 the time in seconds since the Epoch (00:00:00 UTC on January 1, 1970;
 see
 .Xr time 3 ) .
 .Pp
 The
 .Fn localtime
 function converts the time value pointed to by
 .Fa clock ,
 and returns a pointer to a
 .Vt struct tm
 (described below) which contains
 the broken-out time information for the value after adjusting for the current
 time zone (see
 .Xr tzset 3 ) .
 When the specified time translates to a year that will not fit in an
 .Vt int ,
 .Fn localtime
 returns
 .Dv NULL .
 The
 .Fn localtime
 function uses
 .Xr tzset 3
 to initialize time conversion information if
 .Xr tzset 3
 has not already been called by the process.
 .Pp
 After filling in the
 .Vt struct tm ,
 .Fn localtime
 sets the
 .Va tm_isdst Ns 'th
 element of
 .Va tzname
 to a pointer to an ASCII string that is the time zone abbreviation to be
 used with
 .Fn localtime Ns 's
 return value.
 .Pp
 The
 .Fn gmtime
 function similarly converts the time value, but without any time zone
 adjustment, and returns a pointer to a
 .Vt struct tm .
 .Pp
 The
 .Fn ctime
 function
 adjusts the time value for the current time zone in the same manner as
 .Fn localtime ,
 and returns a pointer to a 26-character string of the form:
 .Bd -literal -offset indent
 Thu Nov 24 18:22:48 1986\en\e0
 .Ed
 .Pp
 All the fields have constant width.
 .Pp
 The
 .Fn asctime
 function converts the broken down time in the
 .Vt struct tm
 pointed to by
 .Fa tm
 to the form shown in the example above.
 .Pp
 The
 .Fn ctime_r
 and
 .Fn asctime_r
 functions
 provide the same functionality as
 .Fn ctime
 and
 .Fn asctime
 except the caller must provide the output buffer
 .Fa buf ,
 which must be at least 26 characters long, to store the result in.
 The
 .Fn localtime_r
 and
 .Fn gmtime_r
 functions provide the same functionality as
 .Fn localtime
 and
 .Fn gmtime
 respectively, except the caller must provide the output buffer
 .Fa result .
 .Pp
 The functions
 .Fn mktime
 and
 .Fn timegm
 convert the broken-down time in the
 .Vt struct tm
 pointed to by
 .Fa tm
 into a time value with the same encoding as that of the values
 returned by the
 .Xr time 3
 function (that is, seconds from the Epoch, UTC).
 The
 .Fn mktime
 function interprets the input structure according to the current
 timezone setting (see
 .Xr tzset 3 )
 while the
 .Fn timegm
 function interprets the input structure as representing Universal
 Coordinated Time
 .Pq UTC .
 .Pp
 The original values of the
 .Fa tm_wday
 and
 .Fa tm_yday
 components of the structure are ignored, and the original values of the
 other components are not restricted to their normal ranges, and will be
 normalized if needed.
 For example,
 October 40 is changed into November 9,
 a
 .Fa tm_hour
 of \-1 means 1 hour before midnight,
 .Fa tm_mday
 of 0 means the day preceding the current month, and
 .Fa tm_mon
 of \-2 means 2 months before January of
 .Fa tm_year .
 (A positive or zero value for
 .Fa tm_isdst
 causes
 .Fn mktime
 to presume initially that summer time (for example, Daylight Saving Time)
 is or is not in effect for the specified time, respectively.
 A negative value for
 .Fa tm_isdst
 causes the
 .Fn mktime
 function to attempt to guess whether summer time is in effect for the
 specified time.
 The
 .Fa tm_isdst
 and
 .Fa tm_gmtoff
 members are forced to zero by
 .Fn timegm . )
 .Pp
 On successful completion, the values of the
 .Fa tm_wday
 and
 .Fa tm_yday
 components of the structure are set appropriately, and the other components
 are set to represent the specified calendar time, but with their values
 forced to their normal ranges; the final value of
 .Fa tm_mday
 is not set until
 .Fa tm_mon
 and
 .Fa tm_year
 are determined.
 The
 .Fn mktime
 function
 returns the specified calendar time; if the calendar time cannot be
-represented, it returns \-1;
+represented, it returns \-1 and sets
+.Xr errno 3
+to an appropriate value.
+.Pp
+Note that \-1 is a valid result (representing one second before
+midnight UTC on the evening of 31 December 1969), so this cannot be
+relied upon to indicate success or failure; instead,
+.Fa tm_wday
+and / or
+.Fa tm_yday
+should be set to an out-of-bounds value (e.g. \-1) prior to calling
+.Fn mktime
+or
+.Fn timegm
+and checked after the call.
 .Pp
 The
 .Fn difftime
 function returns the difference in seconds between two time values,
 .Fa time1
 \-
 .Fa time0 .
 .Pp
 External declarations as well as the definition of
 .Vt struct tm
 are in the
 .In time.h
 header.
 The
 .Vt tm
 structure includes at least the following fields:
 .Bd -literal -offset indent
 int tm_sec;	/* seconds (0 - 60) */
 int tm_min;	/* minutes (0 - 59) */
 int tm_hour;	/* hours (0 - 23) */
 int tm_mday;	/* day of month (1 - 31) */
 int tm_mon;	/* month of year (0 - 11) */
 int tm_year;	/* year \- 1900 */
 int tm_wday;	/* day of week (Sunday = 0) */
 int tm_yday;	/* day of year (0 - 365) */
 int tm_isdst;	/* is summer time in effect? */
 char *tm_zone;	/* abbreviation of timezone name */
 long tm_gmtoff;	/* offset from UTC in seconds */
 .Ed
 .Pp
 The
 .Fa tm_isdst
 field is non-zero if summer time is in effect.
 .Pp
 The
 .Fa tm_gmtoff
 field is the offset in seconds of the time represented from UTC,
 with positive values indicating a time zone ahead of UTC (east of the
 Prime Meridian).
 .Sh SEE ALSO
 .Xr date 1 ,
 .Xr clock_gettime 2 ,
 .Xr gettimeofday 2 ,
 .Xr getenv 3 ,
 .Xr time 3 ,
 .Xr tzset 3 ,
 .Xr tzfile 5
 .Sh STANDARDS
 The
 .Fn asctime ,
 .Fn ctime ,
 .Fn difftime ,
 .Fn gmtime ,
 .Fn localtime ,
 and
 .Fn mktime
 functions conform to
 .St -isoC ,
 and conform to
 .St -p1003.1-96
 provided the selected local timezone does not contain a leap-second table
 (see
 .Xr zic 8 ) .
 .Pp
 The
 .Fn asctime_r ,
 .Fn ctime_r ,
 .Fn gmtime_r ,
 and
 .Fn localtime_r
 functions are expected to conform to
 .St -p1003.1-96
 (again provided the selected local timezone does not contain a leap-second
 table).
 .Pp
 The
 .Fn timegm
 function is not specified by any standard; its function cannot be
 completely emulated using the standard functions described above.
 .Sh HISTORY
 This manual page is derived from
 the time package contributed to Berkeley by
 .An Arthur Olson
 and which appeared in
 .Bx 4.3 .
 .Pp
 The functions
 .Fn asctime ,
 .Fn gmtime ,
 and
 .Fn localtime
 first appeared in
 .At v5 ,
 .Fn difftime
 and
 .Fn mktime
 in
 .Bx 4.3 Reno ,
 and
 .Fn timegm
 and
 .Fn timelocal
 in SunOS 4.0.
 .Pp
 The
 .Fn asctime_r ,
 .Fn ctime_r ,
 .Fn gmtime_r
 and
 .Fn localtime_r
 functions have been available since
 .Fx 8.0 .
 .Sh BUGS
 Except for
 .Fn difftime ,
 .Fn mktime ,
 and the
 .Fn \&_r
 variants of the other functions,
 these functions leave their result in an internal static object and return
 a pointer to that object.
 Subsequent calls to these
 function will modify the same object.
 .Pp
 The C Standard provides no mechanism for a program to modify its current
 local timezone setting, and the POSIX-standard
 method is not reentrant.
 (However, thread-safe implementations are provided
 in the POSIX threaded environment.)
 .Pp
 The
 .Va tm_zone
 field of a returned
 .Vt tm
 structure points to a static array of characters,
 which will also be overwritten by any subsequent calls (as well as by
 subsequent calls to
 .Xr tzset 3 ) .
 .Pp
 Use of the external variable
 .Fa tzname
 is discouraged; the
 .Fa tm_zone
 entry in the tm structure is preferred.