diff --git a/core/misc/ajax.es6.js b/core/misc/ajax.es6.js
index 6248e46efe..eb450916d9 100644
--- a/core/misc/ajax.es6.js
+++ b/core/misc/ajax.es6.js
@@ -531,6 +531,29 @@
       if (!drupalSettings.ajaxTrustedUrl[ajax.url] && !Drupal.url.isLocal(ajax.url)) {
         throw new Error(Drupal.t('The callback URL is not local and not trusted: !url', { '!url': ajax.url }));
       }
+
+      // If an Ajax element is a form submission element, perform client-side
+      // validation if the element doesn't explicitly call for a validation
+      // bypass. If the form is invalid:
+      // - If the browser has an implementation of
+      //   HTMLFormElement.reportValidity(), use this to trigger native
+      //   validation messages, otherwise, fall back to triggering a form
+      //   submission.
+      // - Don't generate a response.
+      let $elem = $(this);
+      if ($elem.attr('type') === 'submit' && !$elem.attr('formnovalidate')) {
+        let formElem = $elem.closest('form')[0];
+        if (formElem && !formElem.checkValidity()) {
+          if (typeof formElem.reportValidity === 'function') {
+            formElem.reportValidity();
+          }
+          else {
+            $elem.once(`${event.type}-ajax`).trigger(event.type);
+          }
+          return;
+        }
+      }
+
       return ajax.eventResponse(this, event);
     });
 
diff --git a/core/misc/ajax.js b/core/misc/ajax.js
index 5ea52425be..f7f494ffef 100644
--- a/core/misc/ajax.js
+++ b/core/misc/ajax.js
@@ -252,6 +252,20 @@ function _toConsumableArray(arr) { if (Array.isArray(arr)) { for (var i = 0, arr
       if (!drupalSettings.ajaxTrustedUrl[ajax.url] && !Drupal.url.isLocal(ajax.url)) {
         throw new Error(Drupal.t('The callback URL is not local and not trusted: !url', { '!url': ajax.url }));
       }
+
+      var $elem = $(this);
+      if ($elem.attr('type') === 'submit' && !$elem.attr('formnovalidate')) {
+        var formElem = $elem.closest('form')[0];
+        if (formElem && !formElem.checkValidity()) {
+          if (typeof formElem.reportValidity === 'function') {
+            formElem.reportValidity();
+          } else {
+            $elem.once(event.type + '-ajax').trigger(event.type);
+          }
+          return;
+        }
+      }
+
       return ajax.eventResponse(this, event);
     });