--- a/make/data/tzdata/leapseconds	Tue Sep 24 09:38:14 2019 +0200
+++ b/make/data/tzdata/leapseconds	Tue Sep 24 10:16:00 2019 +0100
@@ -26,36 +26,39 @@
 # This file is in the public domain.
 
 # This file is generated automatically from the data in the public-domain
-# leap-seconds.list file, which can be copied from
+# NIST format leap-seconds.list file, which can be copied from
 # <ftp://ftp.nist.gov/pub/time/leap-seconds.list>
-# or <ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list>
-# or <ftp://tycho.usno.navy.mil/pub/ntp/leap-seconds.list>.
+# or <ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list>.
 # For more about leap-seconds.list, please see
 # The NTP Timescale and Leap Seconds
 # <https://www.eecis.udel.edu/~mills/leap.html>.
 
-# The International Earth Rotation and Reference Systems Service
+# The rules for leap seconds are specified in Annex 1 (Time scales) of:
+# Standard-frequency and time-signal emissions.
+# International Telecommunication Union - Radiocommunication Sector
+# (ITU-R) Recommendation TF.460-6 (02/2002)
+# <https://www.itu.int/rec/R-REC-TF.460-6-200202-I/>.
+# The International Earth Rotation and Reference Systems Service (IERS)
 # periodically uses leap seconds to keep UTC to within 0.9 s of UT1
-# (which measures the true angular orientation of the earth in space)
+# (a proxy for Earth's angle in space as measured by astronomers)
 # and publishes leap second data in a copyrighted file
 # <https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat>.
 # See: Levine J. Coordinated Universal Time and the leap second.
 # URSI Radio Sci Bull. 2016;89(4):30-6. doi:10.23919/URSIRSB.2016.7909995
 # <https://ieeexplore.ieee.org/document/7909995>.
 
-# There were no leap seconds before 1972, because the official mechanism
-# accounting for the discrepancy between atomic time and the earth's rotation
-# did not exist.  The first ("1 Jan 1972") data line in leap-seconds.list
+# There were no leap seconds before 1972, as no official mechanism
+# accounted for the discrepancy between atomic time (TAI) and the earth's
+# rotation.  The first ("1 Jan 1972") data line in leap-seconds.list
 # does not denote a leap second; it denotes the start of the current definition
 # of UTC.
 
-# The correction (+ or -) is made at the given time, so lines
-# will typically look like:
-#	Leap	YEAR	MON	DAY	23:59:60	+	R/S
-# or
-#	Leap	YEAR	MON	DAY	23:59:59	-	R/S
-
-# If the leap second is Rolling (R) the given time is local time (unused here).
+# All leap-seconds are Stationary (S) at the given UTC time.
+# The correction (+ or -) is made at the given time, so in the unlikely
+# event of a negative leap second, a line would look like this:
+# Leap	YEAR	MON	DAY	23:59:59	-	S
+# Typical lines look like this:
+# Leap	YEAR	MON	DAY	23:59:60	+	S
 Leap	1972	Jun	30	23:59:60	+	S
 Leap	1972	Dec	31	23:59:60	+	S
 Leap	1973	Dec	31	23:59:60	+	S
@@ -85,8 +88,8 @@
 Leap	2016	Dec	31	23:59:60	+	S
 
 # POSIX timestamps for the data in this file:
-#updated 1467936000
-#expires 1577491200
+#updated 1467936000 (2016-07-08 00:00:00 UTC)
+#expires 1593302400 (2020-06-28 00:00:00 UTC)
 
-#	Updated through IERS Bulletin C57
-#	File expires on:  28 December 2019
+#	Updated through IERS Bulletin C58
+#	File expires on:  28 June 2020