diff --git a/src/controllers/Items/Sync.php b/src/controllers/Items/Sync.php
index 6490d0bd7b..6b83f88b4d 100644
--- a/src/controllers/Items/Sync.php
+++ b/src/controllers/Items/Sync.php
@@ -56,11 +56,12 @@ public function sync(Base $f3) {
         }
 
         $since = new \DateTime($params['since']);
+        $since->setTimeZone(new \DateTimeZone(date_default_timezone_get()));
 
         $last_update = new \DateTime($this->itemsDao->lastUpdate());
 
         $sync = [
-            'lastUpdate' => $last_update->format('Y-m-d H:i:s'),
+            'lastUpdate' => $last_update->format(\DateTime::ATOM),
         ];
 
         $sinceId = 0;
@@ -72,6 +73,7 @@ public function sync(Base $f3) {
                     $sinceId = $this->itemsDao->lowestIdOfInterest() - 1;
                     // only send 1 day worth of items
                     $notBefore = new \DateTime();
+                    $notBefore->setTimeZone(new \DateTimeZone(date_default_timezone_get()));
                     $notBefore->sub(new \DateInterval('P1D'));
                 }