diff --git a/src/TypeResolver.php b/src/TypeResolver.php
index 2aa31f8..47d6f16 100644
--- a/src/TypeResolver.php
+++ b/src/TypeResolver.php
@@ -239,7 +239,7 @@ private function parseTypes(ArrayIterator $tokens, Context $context, int $parser
                 $resolvedType = new Expression($type);
 
                 $types[] = $resolvedType;
-            } elseif ($parserContext === self::PARSER_IN_ARRAY_EXPRESSION && $token[0] === ')') {
+            } elseif ($parserContext === self::PARSER_IN_ARRAY_EXPRESSION && isset($token[0]) && $token[0] === ')') {
                 break;
             } elseif ($token === '<') {
                 if (count($types) === 0) {
@@ -406,7 +406,7 @@ private function isKeyword(string $type): bool
      */
     private function isPartialStructuralElementName(string $type): bool
     {
-        return ($type[0] !== self::OPERATOR_NAMESPACE) && !$this->isKeyword($type);
+        return (isset($type[0]) && $type[0] !== self::OPERATOR_NAMESPACE) && !$this->isKeyword($type);
     }
 
     /**