Index: lib/libc/stdtime/strptime.3
===================================================================
--- lib/libc/stdtime/strptime.3
+++ lib/libc/stdtime/strptime.3
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\" "
-.Dd October 2, 2014
+.Dd February 28, 2020
 .Dt STRPTIME 3
 .Os
 .Sh NAME
@@ -80,12 +80,22 @@
 are now interpreted as beginning at 1969 per POSIX requirements.
 Years 69-00 are interpreted in the 20th century (1969-2000), years
 01-68 in the 21st century (2001-2068).
+Four-digit year values in
+.Fa \&%Y
+specifier are interpreted as days since year 1900
+as per POSIX requirements.
 The
 .Fa \&%U
 and
 .Fa %W
 format specifiers accept any value within the range 00 to 53.
 .Pp
+The time zone
+.Fa \&%z
+format specifier accepts both RFC 822 (+hhmm) and ISO 8601 (+hhmm +hh:mm +hh Z)
+standard time zone formats.
+The -00, -00:00, -0000 time zone values are also accepted as per RFC 3339.
+.Pp
 If the
 .Fa format
 string does not contain enough conversion specifications to completely
Index: lib/libc/stdtime/strptime.c
===================================================================
--- lib/libc/stdtime/strptime.c
+++ lib/libc/stdtime/strptime.c
@@ -573,26 +573,39 @@
 		case 'z':
 			{
 			int sign = 1;
+			len = 4;	/* RFC 822/ISO 8601 */
 
 			if (*buf != '+') {
 				if (*buf == '-')
 					sign = -1;
+				else if (*buf == 'Z')	/* ISO 8601 Z (UTC) */
+					len = 0;
 				else
 					return (NULL);
 			}
 
 			buf++;
 			i = 0;
-			for (len = 4; len > 0; len--) {
+			for (; len > 0; len--) {
 				if (isdigit_l((unsigned char)*buf, locale)) {
 					i *= 10;
 					i += *buf - '0';
 					buf++;
+				} else if (*buf == ':' && len == 2) {
+					buf++;	/* ISO 8601 +hh:mm */
+					if (isdigit_l((unsigned char)*buf, locale)) {
+						i *= 10;
+						i += *buf - '0';
+						buf++;
+					} else {
+						return (NULL);
+					}
 				} else if (len == 2) {
-					i *= 100;
+					i *= 100;	/* ISO 8601 +hh */
 					break;
-				} else
+				} else {
 					return (NULL);
+				}
 			}
 
 			if (i > 1400 || (sign == -1 && i > 1200) ||