diff --git a/core/misc/ajax.js b/core/misc/ajax.js
--- a/core/misc/ajax.js
+++ b/core/misc/ajax.js
@@ -256,19 +256,23 @@
       ajax.options.data.dialogOptions = elementSettings.dialog;
     }

-    if (ajax.options.url.indexOf('?') === -1) {
-      ajax.options.url += '?';
-    } else {
-      ajax.options.url += '&';
-    }
-
     var wrapper = "drupal_".concat(elementSettings.dialogType || 'ajax');

     if (elementSettings.dialogRenderer) {
       wrapper += ".".concat(elementSettings.dialogRenderer);
     }

-    ajax.options.url += "".concat(Drupal.ajax.WRAPPER_FORMAT, "=").concat(wrapper);
+    var queryParameter = Drupal.ajax.WRAPPER_FORMAT + '=' + wrapper;
+    if (ajax.options.url.indexOf(Drupal.ajax.WRAPPER_FORMAT) === -1) {
+      // Ensure that we have a valid URL by adding ? when no query parameter is
+      // yet available, otherwise append using &.
+      ajax.options.url += (ajax.options.url.indexOf('?') === -1) ? '?' : '&';
+      ajax.options.url += queryParameter;
+    } else {
+      var regexPattern = new RegExp(Drupal.ajax.WRAPPER_FORMAT + '=[^&]*', 'i');
+      ajax.options.url = ajax.options.url.replace(regexPattern, queryParameter);
+    }
+
     $(ajax.element).on(elementSettings.event, function (event) {
       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', {
@@ -671,4 +675,4 @@
       messages.add(response.message, response.messageOptions);
     }
   };
-})(jQuery, window, Drupal, drupalSettings, window.tabbable);
\ No newline at end of file
+})(jQuery, window, Drupal, drupalSettings, window.tabbable);
diff --git a/core/misc/ajax.es6.js b/core/misc/ajax.es6.js
--- a/core/misc/ajax.es6.js
+++ b/core/misc/ajax.es6.js
@@ -569,19 +569,22 @@
       ajax.options.data.dialogOptions = elementSettings.dialog;
     }

-    // Ensure that we have a valid URL by adding ? when no query parameter is
-    // yet available, otherwise append using &.
-    if (ajax.options.url.indexOf('?') === -1) {
-      ajax.options.url += '?';
-    } else {
-      ajax.options.url += '&';
-    }
     // If this element has a dialog type use if for the wrapper if not use 'ajax'.
     let wrapper = `drupal_${elementSettings.dialogType || 'ajax'}`;
     if (elementSettings.dialogRenderer) {
       wrapper += `.${elementSettings.dialogRenderer}`;
     }
-    ajax.options.url += `${Drupal.ajax.WRAPPER_FORMAT}=${wrapper}`;
+
+    const queryParameter = `${Drupal.ajax.WRAPPER_FORMAT}=${wrapper}`;
+    if (ajax.options.url.indexOf(Drupal.ajax.WRAPPER_FORMAT) === -1) {
+      // Ensure that we have a valid URL by adding ? when no query parameter is
+      // yet available, otherwise append using &.
+      ajax.options.url += ajax.options.url.indexOf('?') === -1 ? '?' : '&';
+      ajax.options.url += queryParameter;
+    } else {
+      const regexPattern = new RegExp(`${Drupal.ajax.WRAPPER_FORMAT}=[^&]*`, 'i');
+      ajax.options.url = ajax.options.url.replace(regexPattern, queryParameter);
+    }

     // Bind the ajaxSubmit function to the element event.
     $(ajax.element).on(elementSettings.event, function (event) {