diff --git src/wp-includes/class-wp-customize-manager.php src/wp-includes/class-wp-customize-manager.php
index ec0fa8d..8fd1a67 100644
--- src/wp-includes/class-wp-customize-manager.php
+++ src/wp-includes/class-wp-customize-manager.php
@@ -959,6 +959,10 @@ final class WP_Customize_Manager {
 		// Posts & pages.
 		if ( ! empty( $posts ) ) {
 			foreach ( array_keys( $posts ) as $post_symbol ) {
+				if ( empty( $posts[ $post_symbol ]['post_name'] ) ) {
+					$posts[ $post_symbol ]['post_name'] = sanitize_title( $posts[ $post_symbol ]['post_title'] );
+				}
+
 				$posts[ $post_symbol ]['ID'] = wp_insert_post( wp_slash( array_merge(
 					$posts[ $post_symbol ],
 					array( 'post_status' => 'auto-draft' )