diff --git a/api/modules/session/models/JoinForm.php b/api/modules/session/models/JoinForm.php
index b8b2aff..2676fb2 100644
--- a/api/modules/session/models/JoinForm.php
+++ b/api/modules/session/models/JoinForm.php
@@ -134,7 +134,7 @@ class JoinForm extends Model {
             throw new ForbiddenOperationException('Wrong selected_profile.');
         }
 
-        if (!$isUuid && $account->username !== $selectedProfile) {
+        if (!$isUuid && mb_strtolower($account->username) !== mb_strtolower($selectedProfile)) {
             Session::error(
                 "User with access_token = '{$accessToken}' trying to join with identity = '{$selectedProfile}'," .
                 " but access_token issued to account with username = '{$account->username}'."
diff --git a/tests/codeception/api/functional/sessionserver/JoinLegacyCest.php b/tests/codeception/api/functional/sessionserver/JoinLegacyCest.php
index a04cbc0..27fe28c 100644
--- a/tests/codeception/api/functional/sessionserver/JoinLegacyCest.php
+++ b/tests/codeception/api/functional/sessionserver/JoinLegacyCest.php
@@ -30,6 +30,17 @@ class JoinLegacyCest {
         $this->expectSuccessResponse($I);
     }
 
+    public function joinByOauth2TokenAndDifferentLetterCase(AuthserverSteps $I) {
+        $I->wantTo('join to server by legacy protocol, using legacy authserver access token and different letter case');
+        [$accessToken] = $I->amAuthenticated();
+        $this->route->joinLegacy([
+            'sessionId' => $accessToken,
+            'user' => 'admin',
+            'serverId' => Uuid::uuid(),
+        ]);
+        $this->expectSuccessResponse($I);
+    }
+
     public function joinByNewSessionFormat(AuthserverSteps $I) {
         $I->wantTo('join to server by legacy protocol with new launcher session format, using legacy authserver');
         [$accessToken] = $I->amAuthenticated();