+diff --git a/core/lib/Drupal/Core/Form/FormBuilder.php b/core/lib/Drupal/Core/Form/FormBuilder.php
+index d94b9109b6..028396c909 100644
+--- a/core/lib/Drupal/Core/Form/FormBuilder.php
++++ b/core/lib/Drupal/Core/Form/FormBuilder.php
+@@ -239,7 +239,7 @@ public function buildForm($form_id, FormStateInterface &$form_state) {
+ // should be initialized to empty rather than to ['destination' => 'foo'].
+ $input = $form_state->getUserInput();
+- $input = $form_state->isMethodType('get') ? $request->query->all() : $request->request->all();
++ $input = $request->isMethod('get') ? $request->query->all() : $request->request->all();
+ $form_state->setUserInput($input);
+@@ -560,6 +560,16 @@ public function processForm($form_id, &$form, FormStateInterface &$form_state) {
+ $unprocessed_form = $form;
+ $form = $this->doBuildForm($form_id, $form, $form_state);
++ // Allow an ajax callback while the form is operating in GET mode.
++ // For example when using HOOK_form_views_exposed_form_alter.
++ if ($form_state->isMethodType('get')) {
++ $triggered = $this->requestStack->getCurrentRequest()->request->get('_triggering_element_name');
++ if ($triggered && isset($form[$triggered]) && isset($form[$triggered]['#ajax'])) {
++ $form_state->setTriggeringElement($form[$triggered]);
++ throw new FormAjaxException($form, $form_state);
+ // Only process the input if we have a correct form submission.
+ if ($form_state->isProcessingInput()) {
+ // Form values for programmed form submissions typically do not include a
