diff --git wp-includes/cron.php wp-includes/cron.php
index 8b88c12..871a0df 100644
--- wp-includes/cron.php
+++ wp-includes/cron.php
@@ -23,7 +23,7 @@
 function wp_schedule_single_event( $timestamp, $hook, $args = array()) {
 	// don't schedule a duplicate if there's already an identical event due within 10 minutes of it
 	$next = wp_next_scheduled($hook, $args);
-	if ( $next && abs( $next - $timestamp ) <= 10 * MINUTE_IN_SECONDS ) {
+	if ( ( ! is_numeric( $timestamp ) || $timestamp <= 0 ) || ( $next && abs( $next - $timestamp ) <= 10 * MINUTE_IN_SECONDS ) ) {
 		return;
 	}