diff --git a/Core/snippet-bootstrap.php b/Core/snippet-bootstrap.php
index c36fafda5136..b53df247d3c9 100644
--- a/Core/snippet-bootstrap.php
+++ b/Core/snippet-bootstrap.php
@@ -3,3 +3,5 @@
 use Google\Cloud\Core\Testing\TestHelpers;
 
 TestHelpers::snippetBootstrap();
+
+date_default_timezone_set('UTC');
diff --git a/Core/tests/Unit/TimestampTest.php b/Core/tests/Unit/TimestampTest.php
index 6af178227228..994509debad0 100644
--- a/Core/tests/Unit/TimestampTest.php
+++ b/Core/tests/Unit/TimestampTest.php
@@ -208,4 +208,28 @@ public function timestampArrays()
             ]
         ];
     }
+
+    /**
+     * @dataProvider timezones
+     */
+    public function testTimezones($tz)
+    {
+        $time = new \DateTimeImmutable('now', new \DateTimeZone($tz));
+        $timestamp = new Timestamp($time);
+
+        $utc = $time->setTimeZone(new \DateTimeZone('UTC'));
+        $utcTs = new Timestamp($utc);
+
+        $this->assertEquals($utcTs->formatAsString(), $timestamp->formatAsString());
+    }
+
+    public function timezones()
+    {
+        return [
+            ['America/Detroit'],
+            ['Australia/Sydney'],
+            ['Pacific/Guam'],
+            ['Africa/Johannesburg'],
+        ];
+    }
 }
diff --git a/Core/unit-bootstrap.php b/Core/unit-bootstrap.php
new file mode 100644
index 000000000000..f11c03886df4
--- /dev/null
+++ b/Core/unit-bootstrap.php
@@ -0,0 +1,3 @@
+<?php
+
+date_default_timezone_set('UTC');
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 270f49ac819e..d40ffa8fe25e 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,5 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit colors="true">
+<phpunit
+  bootstrap="./Core/unit-bootstrap.php"
+  colors="true">
   <testsuites>
     <testsuite>
       <directory>*/tests/Unit</directory>