diff --git a/src/govuk/vendor/polyfills/Element/prototype/nextElementSibling.js b/src/govuk/vendor/polyfills/Element/prototype/nextElementSibling.js
index ec3c615496c..35592a91308 100644
--- a/src/govuk/vendor/polyfills/Element/prototype/nextElementSibling.js
+++ b/src/govuk/vendor/polyfills/Element/prototype/nextElementSibling.js
@@ -18,7 +18,7 @@ import '../../Element'
         get: function(){
           var el = this.nextSibling;
           while (el && el.nodeType !== 1) { el = el.nextSibling; }
-          return (el.nodeType === 1) ? el : null;
+          return (el && el.nodeType === 1) ? el : null;
         }
       });
 
diff --git a/src/govuk/vendor/polyfills/Element/prototype/previousElementSibling.js b/src/govuk/vendor/polyfills/Element/prototype/previousElementSibling.js
index 1184a0a3e31..a211fd96f3e 100644
--- a/src/govuk/vendor/polyfills/Element/prototype/previousElementSibling.js
+++ b/src/govuk/vendor/polyfills/Element/prototype/previousElementSibling.js
@@ -16,7 +16,7 @@ import '../../Element'
         get: function(){
           var el = this.previousSibling;
           while (el && el.nodeType !== 1) { el = el.previousSibling; }
-          return (el.nodeType === 1) ? el : null;
+          return (el && el.nodeType === 1) ? el : null;
         }
       });