diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index e43e64c..c839c3f 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -1,4 +1,4 @@
 parameters:
-  level: 3
+  level: 5
   paths:
     - src
diff --git a/src/Json5Decoder.php b/src/Json5Decoder.php
index 0d7209a..5b2da32 100644
--- a/src/Json5Decoder.php
+++ b/src/Json5Decoder.php
@@ -63,7 +63,7 @@ public static function decode(string $json, ?bool $associative = false, int $dep
 
         // Fall back to JSON5 if that fails
         $associative = $associative === true || ($associative === null && $flags & \JSON_OBJECT_AS_ARRAY);
-        $castBigIntToString = $flags & \JSON_BIGINT_AS_STRING;
+        $castBigIntToString = (bool) ($flags & \JSON_BIGINT_AS_STRING);
 
         $decoder = new self($json, $associative, $depth, $castBigIntToString);