diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldWidget/EntityReferenceAutocompleteWidget.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldWidget/EntityReferenceAutocompleteWidget.php
index 11f048e6f8..5a46e00f60 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldWidget/EntityReferenceAutocompleteWidget.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldWidget/EntityReferenceAutocompleteWidget.php
@@ -28,7 +28,7 @@ class EntityReferenceAutocompleteWidget extends WidgetBase {
   public static function defaultSettings() {
     return [
       'match_operator' => 'CONTAINS',
-      'size' => '60',
+      'size' => 60,
       'placeholder' => '',
     ] + parent::defaultSettings();
   }
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceAutocompleteWidgetTest.php b/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceAutocompleteWidgetTest.php
index 511dee6e32..4a39ae6b60 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceAutocompleteWidgetTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceAutocompleteWidgetTest.php
@@ -49,14 +49,22 @@ public function testEntityReferenceAutocompleteWidget() {
     // operator.
     $field_name = 'field_test';
     $this->createEntityReferenceField('node', 'page', $field_name, $field_name, 'node', 'default', ['target_bundles' => ['page']]);
-    entity_get_form_display('node', 'page', 'default')
+    $form_display = entity_get_form_display('node', 'page', 'default')
       ->setComponent($field_name, [
         'type' => 'entity_reference_autocomplete',
         'settings' => [
           'match_operator' => 'CONTAINS',
         ],
-      ])
-      ->save();
+      ]);
+    $form_display->save();
+
+    // To satisfy config schema, the size setting must be an integer, not just
+    // a numeric value. See https://www.drupal.org/node/2885441.
+    $plugin_collections = $form_display->getPluginCollections();
+    $settings = $plugin_collections['widgets']
+      ->get('entity_reference_autocomplete')
+      ->defaultSettings();
+    $this->assertInternalType('integer', $settings['size']);
 
     // Visit the node add page.
     $this->drupalGet('node/add/page');