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 493d6a4f67475e0e..cea4ecb7e97df59b 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 a6423fa749ca47de..e1f580fce7815193 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceAutocompleteWidgetTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceAutocompleteWidgetTest.php
@@ -52,14 +52,18 @@ class EntityReferenceAutocompleteWidgetTest extends WebDriverTestBase {
     // operator.
     $field_name = 'field_test';
     $this->createEntityReferenceField('node', 'page', $field_name, $field_name, 'node', 'default', ['target_bundles' => ['page']]);
-    $display_repository->getFormDisplay('node', 'page')
-      ->setComponent($field_name, [
-        'type' => 'entity_reference_autocomplete',
-        'settings' => [
-          'match_operator' => 'CONTAINS',
-        ],
-      ])
-      ->save();
+    $form_display = $display_repository->getFormDisplay('node', 'page');
+    $form_display->setComponent($field_name, [
+      'type' => 'entity_reference_autocomplete',
+      'settings' => [
+        'match_operator' => 'CONTAINS',
+      ],
+    ]);
+    // To satisfy config schema, the size setting must be an integer, not just
+    // a numeric value. See https://www.drupal.org/node/2885441.
+    $this->assertInternalType('integer', $form_display->getComponent($field_name)['settings']['size']);
+    $form_display->save();
+    $this->assertInternalType('integer', $form_display->getComponent($field_name)['settings']['size']);
 
     // Visit the node add page.
     $this->drupalGet('node/add/page');