diff --git a/src/wp-includes/cron.php b/src/wp-includes/cron.php
index dd348784b9..bd6138256c 100644
--- a/src/wp-includes/cron.php
+++ b/src/wp-includes/cron.php
@@ -79,9 +79,49 @@ function wp_schedule_single_event( $timestamp, $hook, $args = array() ) {
 		return $pre;
 	}
 
-	// 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 ) {
+	/*
+	 * Check for a duplicated event.
+	 *
+	 * Don't schedule an event if there's already an identical event
+	 * within 10 minutes.
+	 *
+	 * When scheduling events within ten minutes of the current time,
+	 * all past identical events are considered duplicates.
+	 *
+	 * When scheduling an event with a past timestamp (ie, before the
+	 * current time) all events scheduled within the next ten minutes
+	 * are considered duplicates.
+	 */
+	$crons     = (array) _get_cron_array();
+	$key       = md5( serialize( $event->args ) );
+	$duplicate = false;
+
+	if ( $event->timestamp < time() + 10 * MINUTE_IN_SECONDS ) {
+		$min_timestamp = 0;
+	} else {
+		$min_timestamp = $event->timestamp - 10 * MINUTE_IN_SECONDS;
+	}
+
+	if ( $event->timestamp < time() ) {
+		$max_timestamp = time() + 10 * MINUTE_IN_SECONDS;
+	} else {
+		$max_timestamp = $event->timestamp + 10 * MINUTE_IN_SECONDS;
+	}
+
+	foreach ( $crons as $event_timestamp => $cron ) {
+		if ( $event_timestamp < $min_timestamp ) {
+			continue;
+		}
+		if ( $event_timestamp > $max_timestamp ) {
+			break;
+		}
+		if ( isset( $cron[ $event->hook ][ $key ] ) ) {
+			$duplicate = true;
+			break;
+		}
+	}
+
+	if ( $duplicate ) {
 		return false;
 	}
 
@@ -107,9 +147,6 @@ function wp_schedule_single_event( $timestamp, $hook, $args = array() ) {
 		return false;
 	}
 
-	$key = md5( serialize( $event->args ) );
-
-	$crons = _get_cron_array();
 	$crons[ $event->timestamp ][ $event->hook ][ $key ] = array(
 		'schedule' => $event->schedule,
 		'args'     => $event->args,
diff --git a/tests/phpunit/tests/cron.php b/tests/phpunit/tests/cron.php
index 8d2f337ed8..3503b1c0d7 100644
--- a/tests/phpunit/tests/cron.php
+++ b/tests/phpunit/tests/cron.php
@@ -596,4 +596,88 @@ class Tests_Cron extends WP_UnitTestCase {
 		$this->assertFalse( wp_get_scheduled_event( $hook, $args, 'Words Fail!' ) );
 
 	}
+
+	/**
+	 * Ensure any past event counts as a duplicate.
+	 *
+	 * @ticket 44818
+	 */
+	function test_duplicate_past_event() {
+		$hook = __FUNCTION__;
+		$args = array( 'arg1' );
+		$ts1  = strtotime( '-14 minutes' );
+		$ts2  = strtotime( '+5 minutes' );
+		$ts3  = strtotime( '-2 minutes' );
+
+		// First event scheduled successfully.
+		$this->assertTrue( wp_schedule_single_event( $ts1, $hook, $args ) );
+
+		// Second event fails.
+		$this->assertFalse( wp_schedule_single_event( $ts2, $hook, $args ) );
+
+		// Third event fails.
+		$this->assertFalse( wp_schedule_single_event( $ts3, $hook, $args ) );
+	}
+
+	/**
+	 * Ensure any near future event counts as a duplicate.
+	 *
+	 * @ticket 44818
+	 */
+	function test_duplicate_near_future_event() {
+		$hook = __FUNCTION__;
+		$args = array( 'arg1' );
+		$ts1  = strtotime( '+4 minutes' );
+		$ts2  = strtotime( '-15 minutes' );
+		$ts3  = strtotime( '+12 minutes' );
+
+		// First event scheduled successfully.
+		$this->assertTrue( wp_schedule_single_event( $ts1, $hook, $args ) );
+
+		// Second event fails.
+		$this->assertFalse( wp_schedule_single_event( $ts2, $hook, $args ) );
+
+		// Third event fails.
+		$this->assertFalse( wp_schedule_single_event( $ts3, $hook, $args ) );
+	}
+
+	/**
+	 * Duplicate future events are disallowed.
+	 *
+	 * @ticket 44818
+	 */
+	function test_duplicate_future_event() {
+		$hook = __FUNCTION__;
+		$args = array( 'arg1' );
+		$ts1  = strtotime( '+15 minutes' );
+		$ts2  = strtotime( '-600 seconds', $ts1 );
+		$ts3  = strtotime( '+600 seconds', $ts1 );
+
+		// First event scheduled successfully.
+		$this->assertTrue( wp_schedule_single_event( $ts1, $hook, $args ) );
+
+		// Events within ten minutes should fail.
+		$this->assertFalse( wp_schedule_single_event( $ts2, $hook, $args ) );
+		$this->assertFalse( wp_schedule_single_event( $ts3, $hook, $args ) );
+	}
+
+	/**
+	 * Future events are allowed.
+	 *
+	 * @ticket 44818
+	 */
+	function test_not_duplicate_future_event() {
+		$hook = __FUNCTION__;
+		$args = array( 'arg1' );
+		$ts1  = strtotime( '+15 minutes' );
+		$ts2  = strtotime( '-601 seconds', $ts1 );
+		$ts3  = strtotime( '+601 seconds', $ts1 );
+
+		// First event scheduled successfully.
+		$this->assertTrue( wp_schedule_single_event( $ts1, $hook, $args ) );
+
+		// Events over ten minutes should work.
+		$this->assertTrue( wp_schedule_single_event( $ts2, $hook, $args ) );
+		$this->assertTrue( wp_schedule_single_event( $ts3, $hook, $args ) );
+	}
 }