diff --git a/code/controllers/ModelAsController.php b/code/controllers/ModelAsController.php
index fd7d0654..175c9353 100644
--- a/code/controllers/ModelAsController.php
+++ b/code/controllers/ModelAsController.php
@@ -47,9 +47,9 @@ class ModelAsController extends Controller implements NestedController {
 			$this->getResponse()->redirect(Controller::join_links(
 				Director::absoluteBaseURL(),
 				'dev/build',
-				'?' . array(
+				'?' . http_build_query(array(
 					'returnURL' => isset($_GET['url']) ? $_GET['url'] : null,
-				)
+				))
 			));
 		}
 	}
diff --git a/code/controllers/RootURLController.php b/code/controllers/RootURLController.php
index 2afce1a1..59d4df7e 100644
--- a/code/controllers/RootURLController.php
+++ b/code/controllers/RootURLController.php
@@ -115,9 +115,9 @@ class RootURLController extends Controller {
 			$this->getResponse()->redirect(Controller::join_links(
 				Director::absoluteBaseURL(),
 				'dev/build',
-				'?' . array(
+				'?' . http_build_query(array(
 					'returnURL' => isset($_GET['url']) ? $_GET['url'] : null,
-				)
+				))
 			));
 		}
 	}