core/modules/media/src/Form/MediaSettingsForm.php | 7 ++++++-
 core/modules/system/system.install                | 1 +
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/core/modules/media/src/Form/MediaSettingsForm.php b/core/modules/media/src/Form/MediaSettingsForm.php
index 6d90e36ee4..b70aa19d24 100644
--- a/core/modules/media/src/Form/MediaSettingsForm.php
+++ b/core/modules/media/src/Form/MediaSettingsForm.php
@@ -117,8 +117,13 @@ public function buildForm(array $form, FormStateInterface $form_state) {
    * {@inheritdoc}
    */
   public function submitForm(array &$form, FormStateInterface $form_state) {
+    $iframe_domain = $form_state->getValue('iframe_domain');
+    // The empty string is not a valid URI, but NULL is allowed.
+    if ($iframe_domain === '') {
+      $iframe_domain = NULL;
+    }
     $this->config('media.settings')
-      ->set('iframe_domain', $form_state->getValue('iframe_domain'))
+      ->set('iframe_domain', $iframe_domain)
       ->set('standalone_url', $form_state->getValue('standalone_url'))
       ->save();
 
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index d5c4921f07..fae06ecc27 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -1843,4 +1843,5 @@ function system_update_10101(&$sandbox = NULL) {
       'not null' => TRUE,
     ]);
   }
+
 }