diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 9400781..9de6713 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -29,7 +29,7 @@ jobs:
         continue-on-error: ${{ !matrix.stable }}
         strategy:
             matrix:
-                php: ['8.0', 8.1', '8.2', '8.3']
+                php: ['8.0', '8.1', '8.2', '8.3','8.4']
                 stable: [true]
                 coverage: [true]
                 composer-flags: ['']
diff --git a/composer.json b/composer.json
index f650976..088c1b4 100644
--- a/composer.json
+++ b/composer.json
@@ -25,7 +25,7 @@
     },
     "require-dev": {
         "mikehaertl/php-shellcommand": "^1.7.0",
-        "phpstan/phpstan": "^1.10.57",
+        "phpstan/phpstan": "^2.0",
         "scrutinizer/ocular": "^1.9",
         "squizlabs/php_codesniffer": "^3.8.1",
         "symfony/finder": "^6.0|^7.0",
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);