diff --git a/wp-admin/includes/class-wp-site-health.php b/wp-admin/includes/class-wp-site-health.php
index 605f194ca3..62f089b941 100644
--- a/wp-admin/includes/class-wp-site-health.php
+++ b/wp-admin/includes/class-wp-site-health.php
@@ -1015,6 +1015,46 @@ class WP_Site_Health {
 		return $result;
 	}
 
+	/**
+	 * Test if the PHP default timezone is set to UTC.
+	 *
+	 * @since 5.3.1
+	 *
+	 * @return array The test results.
+	 */
+	public function get_test_php_default_timezone() {
+		$result = array(
+			'label'       => __( 'PHP default timezone is valid' ),
+			'status'      => 'good',
+			'badge'       => array(
+				'label' => __( 'Performance' ),
+				'color' => 'blue',
+			),
+			'description' => sprintf(
+				'<p>%s</p>',
+				__( 'PHP default timezone was configured by WordPress on loading. This is necessary for correct calculations of dates and times.' )
+			),
+			'test'        => 'php_default_timezone',
+		);
+
+		if ( 'UTC' !== date_default_timezone_get() ) {
+			$result['status'] = 'critical';
+
+			$result['label'] = __( 'PHP default timezone is invalid' );
+
+			$result['description'] = sprintf(
+				'<p>%s</p>',
+				sprintf(
+					/* translators: %s: date_default_timezone_set() */
+					__( 'PHP default timezone was changed after WordPress loading by a %s function call. This interferes with correct calculations of dates and times.' ),
+					'<code>date_default_timezone_set()</code>'
+				)
+			);
+		}
+
+		return $result;
+	}
+
 	/**
 	 * Test if the SQL server is up to date.
 	 *
@@ -1842,51 +1882,55 @@ class WP_Site_Health {
 	public static function get_tests() {
 		$tests = array(
 			'direct' => array(
-				'wordpress_version' => array(
+				'wordpress_version'    => array(
 					'label' => __( 'WordPress Version' ),
 					'test'  => 'wordpress_version',
 				),
-				'plugin_version'    => array(
+				'plugin_version'       => array(
 					'label' => __( 'Plugin Versions' ),
 					'test'  => 'plugin_version',
 				),
-				'theme_version'     => array(
+				'theme_version'        => array(
 					'label' => __( 'Theme Versions' ),
 					'test'  => 'theme_version',
 				),
-				'php_version'       => array(
+				'php_version'          => array(
 					'label' => __( 'PHP Version' ),
 					'test'  => 'php_version',
 				),
-				'sql_server'        => array(
-					'label' => __( 'Database Server version' ),
-					'test'  => 'sql_server',
-				),
-				'php_extensions'    => array(
+				'php_extensions'       => array(
 					'label' => __( 'PHP Extensions' ),
 					'test'  => 'php_extensions',
 				),
-				'utf8mb4_support'   => array(
+				'php_default_timezone' => array(
+					'label' => __( 'PHP Default Timezone' ),
+					'test'  => 'php_default_timezone',
+				),
+				'sql_server'           => array(
+					'label' => __( 'Database Server version' ),
+					'test'  => 'sql_server',
+				),
+				'utf8mb4_support'      => array(
 					'label' => __( 'MySQL utf8mb4 support' ),
 					'test'  => 'utf8mb4_support',
 				),
-				'https_status'      => array(
+				'https_status'         => array(
 					'label' => __( 'HTTPS status' ),
 					'test'  => 'https_status',
 				),
-				'ssl_support'       => array(
+				'ssl_support'          => array(
 					'label' => __( 'Secure communication' ),
 					'test'  => 'ssl_support',
 				),
-				'scheduled_events'  => array(
+				'scheduled_events'     => array(
 					'label' => __( 'Scheduled events' ),
 					'test'  => 'scheduled_events',
 				),
-				'http_requests'     => array(
+				'http_requests'        => array(
 					'label' => __( 'HTTP Requests' ),
 					'test'  => 'http_requests',
 				),
-				'debug_enabled'     => array(
+				'debug_enabled'        => array(
 					'label' => __( 'Debugging enabled' ),
 					'test'  => 'is_in_debug_mode',
 				),
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 5080d0f0d9..e6058c8fd6 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3.1-alpha-46796';
+$wp_version = '5.3.1-alpha-46798';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.