diff --git a/.env/0-sandbox.php b/.env/0-sandbox.php
index d36c4d2..e7ccbdb 100644
--- a/.env/0-sandbox.php
+++ b/.env/0-sandbox.php
@@ -13,3 +13,12 @@ namespace {
 	function bump_stats_extra( $name, $value, $views = 1 ) {
 	}
 }
+
+namespace WordPressdotorg\MU_Plugins\Helpers {
+	/**
+	 * Stub.
+	 */
+	function natural_language_join( array $list, $conjunction = 'and' ): string {
+		return implode( ', ', $list );
+	}
+}