diff --git a/CHANGELOG.md b/CHANGELOG.md
index 86882535fb..bf851ce0f6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@
 
 ### Fixes
 
+- [Pull request #1745: Update vendor polyfills to match upstream](https://github.com/alphagov/govuk-frontend/pull/1745).
 - [Pull request #1724: Fix fallback logo being detected by Google Chrome's image description feature](https://github.com/alphagov/govuk-frontend/pull/1724).
 
 ## 3.5.0 (Feature release)
diff --git a/src/govuk/vendor/polyfills/Element/prototype/closest.js b/src/govuk/vendor/polyfills/Element/prototype/closest.js
index 6ed55020fb..45d193e108 100644
--- a/src/govuk/vendor/polyfills/Element/prototype/closest.js
+++ b/src/govuk/vendor/polyfills/Element/prototype/closest.js
@@ -9,7 +9,7 @@ import './matches'
 
   if (detect) return
 
-    // Polyfill from https://raw.githubusercontent.com/Financial-Times/polyfill-service/1f3c09b402f65bf6e393f933a15ba63f1b86ef1f/packages/polyfill-library/polyfills/Element/prototype/closest/polyfill.js
+  // Polyfill from https://raw.githubusercontent.com/Financial-Times/polyfill-service/1f3c09b402f65bf6e393f933a15ba63f1b86ef1f/packages/polyfill-library/polyfills/Element/prototype/closest/polyfill.js
   Element.prototype.closest = function closest(selector) {
     var node = this;
 
diff --git a/src/govuk/vendor/polyfills/Element/prototype/nextElementSibling.js b/src/govuk/vendor/polyfills/Element/prototype/nextElementSibling.js
index 2265654089..72ff79caa7 100644
--- a/src/govuk/vendor/polyfills/Element/prototype/nextElementSibling.js
+++ b/src/govuk/vendor/polyfills/Element/prototype/nextElementSibling.js
@@ -3,26 +3,20 @@ import '../../Element'
 
 (function(undefined) {
 
-    // Detection from https://github.com/Financial-Times/polyfill-service/pull/1062/files#diff-b09a5d2acf3314b46a6c8f8d0c31b85c
+    // Detection from https://raw.githubusercontent.com/Financial-Times/polyfill-library/master/polyfills/Element/prototype/nextElementSibling/detect.js
     var detect = (
-      'Element' in this && "nextElementSibling" in document.documentElement
+      'document' in this && "nextElementSibling" in document.documentElement
     )
 
     if (detect) return
 
-
-    (function (global) {
-
-      // There is no polyfill in polyfill-library (https://github.com/Financial-Times/polyfill-library/issues/338)
-      // So we source this from https://github.com/Alhadis/Snippets/blob/e09b4dfb7ffc9e250bc28319051e39ead3e5f70a/js/polyfills/IE8-child-elements.js#L28-L33
-      Object.defineProperty(Element.prototype, "nextElementSibling", {
-        get: function(){
-          var el = this.nextSibling;
-          while (el && el.nodeType !== 1) { el = el.nextSibling; }
-          return el;
-        }
-      });
-
-    }(this));
+    // Polyfill from https://raw.githubusercontent.com/Financial-Times/polyfill-library/master/polyfills/Element/prototype/nextElementSibling/polyfill.js
+    Object.defineProperty(Element.prototype, "nextElementSibling", {
+      get: function(){
+        var el = this.nextSibling;
+        while (el && el.nodeType !== 1) { el = el.nextSibling; }
+        return el;
+      }
+    });
 
 }).call('object' === typeof window && window || 'object' === typeof self && self || 'object' === typeof global && global || {});
diff --git a/src/govuk/vendor/polyfills/Element/prototype/previousElementSibling.js b/src/govuk/vendor/polyfills/Element/prototype/previousElementSibling.js
index a499550551..daeef5ff60 100644
--- a/src/govuk/vendor/polyfills/Element/prototype/previousElementSibling.js
+++ b/src/govuk/vendor/polyfills/Element/prototype/previousElementSibling.js
@@ -3,24 +3,20 @@ import '../../Element'
 
 (function(undefined) {
 
-    // Detection from https://github.com/Financial-Times/polyfill-service/pull/1062/files#diff-a162235fbc9c0dd40d4032265f44942e
+    // Detection from https://raw.githubusercontent.com/Financial-Times/polyfill-library/master/polyfills/Element/prototype/previousElementSibling/detect.js
     var detect = (
-      'Element' in this && 'previousElementSibling' in document.documentElement
+      'document' in this && "previousElementSibling" in document.documentElement
     )
 
     if (detect) return
 
-    (function (global) {
-      // There is no polyfill in polyfill-library (https://github.com/Financial-Times/polyfill-library/issues/338)
-      // So we source this from https://github.com/Alhadis/Snippets/blob/e09b4dfb7ffc9e250bc28319051e39ead3e5f70a/js/polyfills/IE8-child-elements.js#L35-L40
-      Object.defineProperty(Element.prototype, 'previousElementSibling', {
-        get: function(){
-          var el = this.previousSibling;
-          while (el && el.nodeType !== 1) { el = el.previousSibling; }
-          return el;
-        }
-      });
-
-    }(this));
+    // Polyfill from https://raw.githubusercontent.com/Financial-Times/polyfill-library/master/polyfills/Element/prototype/previousElementSibling/polyfill.js
+    Object.defineProperty(Element.prototype, 'previousElementSibling', {
+      get: function(){
+        var el = this.previousSibling;
+        while (el && el.nodeType !== 1) { el = el.previousSibling; }
+        return el;
+      }
+    });
 
 }).call('object' === typeof window && window || 'object' === typeof self && self || 'object' === typeof global && global || {});