Index: src/wp-includes/cron.php
===================================================================
--- src/wp-includes/cron.php	(revision 29337)
+++ src/wp-includes/cron.php	(working copy)
@@ -107,21 +107,27 @@
 	$interval = 0;
 
 	// First we try to get it from the schedule
-	if ( 0 == $interval )
+	if ( isset( $schedules[ $recurrence ] ) ) {
 		$interval = $schedules[$recurrence]['interval'];
+	}
+
 	// Now we try to get it from the saved interval in case the schedule disappears
-	if ( 0 == $interval )
+	if ( 0 == $interval ) {
 		$interval = $crons[$timestamp][$hook][$key]['interval'];
+	}
+
 	// Now we assume something is wrong and fail to schedule
-	if ( 0 == $interval )
+	if ( 0 == $interval ) {
 		return false;
+	}
 
 	$now = time();
 
-	if ( $timestamp >= $now )
+	if ( $timestamp >= $now ) {
 		$timestamp = $now + $interval;
-	else
+	} else {
 		$timestamp = $now + ($interval - (($now - $timestamp) % $interval));
+	}
 
 	wp_schedule_event( $timestamp, $recurrence, $hook, $args );
 }