diff --git a/app/controllers/course/room_requests.php b/app/controllers/course/room_requests.php
index 3250ba2d5809861bc0ab2614eb550232de548675..464404fac1890b11f9a9beefa0007023f04329d3 100644
--- a/app/controllers/course/room_requests.php
+++ b/app/controllers/course/room_requests.php
@@ -607,7 +607,7 @@ class Course_RoomRequestsController extends AuthenticatedController
             CSRFProtection::verifyUnsafeRequest();
 
             $this->request->user_id = $this->current_user->id;
-            $this->preparation_time = Request::get('preparation_time');
+            $this->preparation_time = Request::int('preparation_time', 0);
             $this->request->preparation_time = $this->preparation_time * 60;
             $this->request->comment = Request::get('comment');
 
diff --git a/app/controllers/course/timesrooms.php b/app/controllers/course/timesrooms.php
index a00e266b2ccee2d0f7d4ebb0f49778bbbf45dc56..7e3d4596d4febb92e9ff40bda9f2c8d1e0c17cb8 100644
--- a/app/controllers/course/timesrooms.php
+++ b/app/controllers/course/timesrooms.php
@@ -458,7 +458,7 @@ class Course_TimesroomsController extends AuthenticatedController
             //has to be recereated, even if the room option
             //is set to "nochange".
             $room_id = null;
-            $preparation_time = Request::get('preparation_time');
+            $preparation_time = Request::int('preparation_time', 0);
             if (Request::option('room') == 'room') {
                 $room_id = Request::get('room_id');
                 if ($preparation_time > $max_preparation_time) {
diff --git a/app/controllers/resources/room_request.php b/app/controllers/resources/room_request.php
index 52a93db1e9a4d7482949e73cacb65de62ed3c60b..e2b476671d55e3c49e5ee475c53a20d91bf97cfc 100644
--- a/app/controllers/resources/room_request.php
+++ b/app/controllers/resources/room_request.php
@@ -963,7 +963,7 @@ class Resources_RoomRequestController extends AuthenticatedController
             $this->begin_time_str = Request::get('begin_time');
             $this->end_date_str = Request::get('end_date');
             $this->end_time_str = Request::get('end_time');
-            $this->preparation_time = Request::get('preparation_time');
+            $this->preparation_time = Request::int('preparation_time', 0);
 
             if (!$this->begin_date_str) {
                 PageLayout::postError(