diff --git a/system/I18n/Time.php b/system/I18n/Time.php
index 64b4d350e8fd..dd97815f66cf 100644
--- a/system/I18n/Time.php
+++ b/system/I18n/Time.php
@@ -82,7 +82,7 @@ public function __construct(?string $time = null, $timezone = null, ?string $loc
         // If a test instance has been provided, use it instead.
         if ($time === '' && static::$testNow instanceof self) {
             $timezone = $timezone ?: static::$testNow->getTimezone();
-            $time     = (string) static::$testNow->toDateTimeString();
+            $time     = static::$testNow->format('Y-m-d H:i:s');
         }
 
         $timezone       = $timezone ?: date_default_timezone_get();
diff --git a/tests/system/I18n/TimeTest.php b/tests/system/I18n/TimeTest.php
index 03f142479478..7571f66eca99 100644
--- a/tests/system/I18n/TimeTest.php
+++ b/tests/system/I18n/TimeTest.php
@@ -1058,4 +1058,18 @@ public function testUnserializeTimeObject()
         $this->assertTrue($time2->equals($time1));
         $this->assertNotSame($time1, $time2);
     }
+
+    public function testSetTestNowWithFaLocale()
+    {
+        $currentLocale = Locale::getDefault();
+        Locale::setDefault('fa');
+
+        Time::setTestNow('2017/03/10 12:00', 'Asia/Tokyo');
+
+        $now = Time::now()->format('c');
+
+        $this->assertSame('2017-03-10T12:00:00+09:00', $now);
+
+        Locale::setDefault($currentLocale);
+    }
 }