diff --git a/wp-includes/class-wp-customize-manager.php b/wp-includes/class-wp-customize-manager.php
index 256e68a036..ed8c76df24 100644
--- a/wp-includes/class-wp-customize-manager.php
+++ b/wp-includes/class-wp-customize-manager.php
@@ -2304,7 +2304,7 @@ final class WP_Customize_Manager {
 			if ( ! is_wp_error( $validity ) ) {
 				/** This filter is documented in wp-includes/class-wp-customize-setting.php */
 				$late_validity = apply_filters( "customize_validate_{$setting->id}", new WP_Error(), $unsanitized_value, $setting );
-				if ( $late_validity->has_errors() ) {
+				if ( is_wp_error( $late_validity ) && $late_validity->has_errors() ) {
 					$validity = $late_validity;
 				}
 			}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 10c644bd31..c535f88be9 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.0-alpha-43577';
+$wp_version = '5.0-alpha-43578';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.