diff --git a/src/lib/isISO8601.js b/src/lib/isISO8601.js
index 6eea9ae27..00d468efc 100644
--- a/src/lib/isISO8601.js
+++ b/src/lib/isISO8601.js
@@ -2,9 +2,9 @@ import assertString from './util/assertString';
 
 /* eslint-disable max-len */
 // from http://goo.gl/0ejHHW
-const iso8601 = /^([\+-]?\d{4}(?!\d{2}\b))((-?)((0[1-9]|1[0-2])(\3([12]\d|0[1-9]|3[01]))?|W(0[1-9]|[1-4]\d|5[0-3])(-?[1-7])?|(00[1-9]|0[1-9]\d|[12]\d{2}|3([0-5]\d|6[0-6])))([T\s]((([01]\d|2[0-3])((:?)[0-5]\d)?|24:?00)([\.,]\d+(?!:))?)?(\17[0-5]\d([\.,]\d+)?)?([zZ]|([\+-])([01]\d|2[0-3]):?([0-5]\d)?)?)?)?$/;
+const iso8601 = /^([\+-]?\d{4}(?!\d{2}\b))((-?)((0[1-9]|1[0-2])(\3([12]\d|0[1-9]|3[01]))?|W(0[1-9]|[1-4]\d|5[0-3])(-?[1-7])?|(00[1-9]|0[1-9]\d|[12]\d{2}|3([0-5]\d|6[0-6])))([T\s]((([01]\d|2[0-3]|24(?=:?00)(?!:?00:?(?:0[1-9]|[1-5]\d)))((:?)[0-5]\d)?)([\.,]\d+(?!:))?)?(\17[0-5]\d([\.,]\d+)?)?([zZ]|([\+-])([01]\d|2[0-3]):?([0-5]\d)?)?)?)?$/;
 // same as above, except with a strict 'T' separator between date and time
-const iso8601StrictSeparator = /^([\+-]?\d{4}(?!\d{2}\b))((-?)((0[1-9]|1[0-2])(\3([12]\d|0[1-9]|3[01]))?|W(0[1-9]|[1-4]\d|5[0-3])(-?[1-7])?|(00[1-9]|0[1-9]\d|[12]\d{2}|3([0-5]\d|6[0-6])))([T]((([01]\d|2[0-3])((:?)[0-5]\d)?|24:?00)([\.,]\d+(?!:))?)?(\17[0-5]\d([\.,]\d+)?)?([zZ]|([\+-])([01]\d|2[0-3]):?([0-5]\d)?)?)?)?$/;
+const iso8601StrictSeparator = /^([\+-]?\d{4}(?!\d{2}\b))((-?)((0[1-9]|1[0-2])(\3([12]\d|0[1-9]|3[01]))?|W(0[1-9]|[1-4]\d|5[0-3])(-?[1-7])?|(00[1-9]|0[1-9]\d|[12]\d{2}|3([0-5]\d|6[0-6])))([T]((([01]\d|2[0-3]|24(?=:?00)(?!:?00:?(?:0[1-9]|[1-5]\d)))((:?)[0-5]\d)?)([\.,]\d+(?!:))?)?(\17[0-5]\d([\.,]\d+)?)?([zZ]|([\+-])([01]\d|2[0-3]):?([0-5]\d)?)?)?)?$/;
 /* eslint-enable max-len */
 const isValidDate = (str) => {
   // str must have passed the ISO8601 check
diff --git a/test/validators.test.js b/test/validators.test.js
index 98d2a12ff..258d3ca96 100644
--- a/test/validators.test.js
+++ b/test/validators.test.js
@@ -12362,6 +12362,8 @@ describe('Validators', () => {
     '20090621T0545Z',
     '2007-04-06T00:00',
     '2007-04-05T24:00',
+    '2007-04-05T24:00:00',
+    '20070405T240000',
     '2010-02-18T16:23:48.5',
     '2010-02-18T16:23:48,444',
     '2010-02-18T16:23:48,3-06:00',
@@ -12383,6 +12385,10 @@ describe('Validators', () => {
     '2009367',
     '2009-',
     '2007-04-05T24:50',
+    '2007-04-05T24:00:30',
+    '20070405T240030',
+    '2007-04-05T2400:30',
+    '2007-04-05T24:0030',
     '2009-000',
     '2009-M511',
     '2009M511',
@@ -12483,6 +12489,8 @@ describe('Validators', () => {
         '20090621T0545Z',
         '2007-04-06T00:00',
         '2007-04-05T24:00',
+        '2007-04-05T24:00:00',
+        '20070405T240000',
         '2010-02-18T16:23:48.5',
         '2010-02-18T16:23:48,444',
         '2010-02-18T16:23:48,3-06:00',
@@ -12500,6 +12508,10 @@ describe('Validators', () => {
         '2009367',
         '2009-',
         '2007-04-05T24:50',
+        '2007-04-05T24:00:30',
+        '20070405T240030',
+        '2007-04-05T2400:30',
+        '2007-04-05T24:0030',
         '2009-000',
         '2009-M511',
         '2009M511',