diff --git a/wp-admin/custom-header.php b/wp-admin/custom-header.php
index b9aecf2485..85238bf21c 100644
--- a/wp-admin/custom-header.php
+++ b/wp-admin/custom-header.php
@@ -1321,7 +1321,12 @@ wp_nonce_field( 'custom-header-options', '_wpnonce-custom-header-options' ); ?>
 	 * @param WP_Customize_Manager $wp_customize Customize manager.
 	 */
 	public function customize_set_last_used( $wp_customize ) {
-		$data = $wp_customize->get_setting( 'header_image_data' )->post_value();
+
+		$header_image_data_setting = $wp_customize->get_setting( 'header_image_data' );
+		if ( ! $header_image_data_setting ) {
+			return;
+		}
+		$data = $header_image_data_setting->post_value();
 
 		if ( ! isset( $data['attachment_id'] ) ) {
 			return;
diff --git a/wp-includes/version.php b/wp-includes/version.php
index c51f719d6f..bc8ff25740 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9-alpha-40934';
+$wp_version = '4.9-alpha-40935';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.