diff --git a/apps/settings/lib/Controller/UsersController.php b/apps/settings/lib/Controller/UsersController.php
index d6410810d8..9f832a5ec4 100644
--- a/apps/settings/lib/Controller/UsersController.php
+++ b/apps/settings/lib/Controller/UsersController.php
@@ -343,6 +343,7 @@ class UsersController extends Controller {
 									$twitter,
 									$twitterScope
 	) {
+		$email = strtolower($email);
 		if (!empty($email) && !$this->mailer->validateMailAddress($email)) {
 			return new DataResponse(
 				[
@@ -422,7 +423,7 @@ class UsersController extends Controller {
 			}
 		}
 		$oldEmailAddress = $user->getEMailAddress();
-		$oldEmailAddress = is_null($oldEmailAddress) ? '' : $oldEmailAddress;
+		$oldEmailAddress = is_null($oldEmailAddress) ? '' : strtolower($oldEmailAddress);
 		if (isset($data[AccountManager::PROPERTY_EMAIL]['value'])
 			&& $oldEmailAddress !== $data[AccountManager::PROPERTY_EMAIL]['value']
 		) {