Index: src/wp-includes/default-constants.php
===================================================================
--- src/wp-includes/default-constants.php	(revision 33652)
+++ src/wp-includes/default-constants.php	(working copy)
@@ -101,6 +101,7 @@
 	define( 'HOUR_IN_SECONDS',   60 * MINUTE_IN_SECONDS );
 	define( 'DAY_IN_SECONDS',    24 * HOUR_IN_SECONDS   );
 	define( 'WEEK_IN_SECONDS',    7 * DAY_IN_SECONDS    );
+	define( 'MONTH_IN_SECONDS',  30 * DAY_IN_SECONDS    );
 	define( 'YEAR_IN_SECONDS',  365 * DAY_IN_SECONDS    );
 }