diff --git a/core/lib/Drupal/Component/Datetime/DateTimePlus.php b/core/lib/Drupal/Component/Datetime/DateTimePlus.php
index 0158eac..dfec5a1 100644
--- a/core/lib/Drupal/Component/Datetime/DateTimePlus.php
+++ b/core/lib/Drupal/Component/Datetime/DateTimePlus.php
@@ -246,11 +246,12 @@ public static function createFromFormat($format, $time, $timezone = NULL, $setti
   /**
    * Constructs a date object set to a requested date and timezone.
    *
-   * @param string $time
-   *   (optional) A date/time string. Defaults to 'now'.
+   * @param mixed $time
+   *   (optional) A \DateTime object or date/time string. Defaults to 'now'.
    * @param mixed $timezone
    *   (optional) \DateTimeZone object, time zone string or NULL. NULL uses the
-   *   default system time zone. Defaults to NULL.
+   *   default system time zone. Defaults to NULL. This parameter is ignored
+   *   if $time is a \DateTime object.
    * @param array $settings
    *   (optional) Keyed array of settings. Defaults to empty array.
    *   - langcode: (optional) String two letter language code used to control
@@ -278,6 +279,15 @@ public function __construct($time = 'now', $timezone = NULL, $settings = []) {
 
       if (empty($this->errors)) {
         $this->dateTimeObject = new \DateTime($prepared_time, $prepared_timezone);
+
+        // If $time is a DateTimePlus object, then its time zone is used
+        // and $timezone is ignored. If $prepared_timezone isn't NULL, then
+        // set the time zone to handle cases where \DateTime::__construct()
+        // ignored this parameter.
+        // @see http://php.net/manual/en/datetime.construct.php
+        if (!($time instanceof DateTimePlus) && $prepared_timezone !== NULL) {
+          $this->dateTimeObject->setTimezone($prepared_timezone);
+        }
       }
     }
     catch (\Exception $e) {
diff --git a/core/tests/Drupal/Tests/Component/Datetime/DateTimePlusTest.php b/core/tests/Drupal/Tests/Component/Datetime/DateTimePlusTest.php
index e50e4c4..3b376db 100644
--- a/core/tests/Drupal/Tests/Component/Datetime/DateTimePlusTest.php
+++ b/core/tests/Drupal/Tests/Component/Datetime/DateTimePlusTest.php
@@ -264,7 +264,7 @@ public function testInvalidDates($input, $timezone, $format, $message, $class) {
   public function testDateTimezone($input, $timezone, $expected_timezone, $message) {
     $date = new DateTimePlus($input, $timezone);
     $timezone = $date->getTimezone()->getName();
-    $this->assertEquals($timezone, $expected_timezone, $message);
+    $this->assertEquals($expected_timezone, $timezone, $message);
   }
 
   /**
@@ -470,6 +470,10 @@ public function providerTestDateTimezone() {
       [$date_string, new \DateTimeZone('Australia/Canberra'), 'Australia/Canberra', 'DateTimePlus uses the specified timezone if provided.'],
       // Create a date object with another date object.
       [new DateTimePlus('now', 'Pacific/Midway'), NULL, 'Pacific/Midway', 'DateTimePlus uses the specified timezone if provided.'],
+      // Create a date object from a string with an explicit time zone offset, and a specified time zone.
+      ['2007-01-31T21:00:00-05:00', 'America/New_York', 'America/New_York', 'DateTimePlus uses the specified timezone if provided.'],
+      // Create a date object from a string with an explicit time zone offset, and an specified time zone.
+      ['2007-01-31T21:00:00-05:00', NULL, $system_timezone, 'DateTimePlus uses the system timezone when there is no site timezone.'],
     ];
   }