diff --git a/src/Validator/Format/FrontierFormatValidator.php b/src/Validator/Format/FrontierFormatValidator.php
index a0ef4c6..de78354 100644
--- a/src/Validator/Format/FrontierFormatValidator.php
+++ b/src/Validator/Format/FrontierFormatValidator.php
@@ -46,7 +46,7 @@ private function validateFrontierUniques(Deck $deck, array $cardsData): array
                 continue;
             }
 
-            $gameplayFormats = $data['gameplayFormat'] ?? [];
+            $gameplayFormats = array_map('strtolower', $data['gameplayFormat'] ?? []);
             if (!in_array(self::GAMEPLAY_FORMAT_KEY, $gameplayFormats, true)) {
                 $errors[] = sprintf('Unique card "%s" is not part of the Frontier format allowlist.', $this->getCardName($data));
             }