diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index d948369..3bf2aea 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -94,6 +94,7 @@ jobs:
     strategy:
       matrix:
         php:
+          - '5.3'
           - '5.4'
           - '5.5'
           - '5.6'
diff --git a/README.md b/README.md
index 68c99c1..6fe783b 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ Additionally `blame` can be used to show commits that introduced the breakage.
 
 Running parallel jobs in PHP is inspired by Nette framework tests.
 
-The application is officially supported for use with PHP 5.4 to 8.0.
+The application is officially supported for use with PHP 5.3 to 8.0.
 
 ## Table of contents
 
diff --git a/composer.json b/composer.json
index ae978fd..6bc745f 100644
--- a/composer.json
+++ b/composer.json
@@ -10,7 +10,7 @@
         }
     ],
     "require": {
-        "php": ">=5.4.0",
+        "php": ">=5.3.0",
         "ext-json": "*"
     },
     "replace": {
diff --git a/parallel-lint b/parallel-lint
index 0d77fdb..cdbcab9 100755
--- a/parallel-lint
+++ b/parallel-lint
@@ -30,19 +30,19 @@ of the authors and should not be interpreted as representing official policies,
 either expressed or implied, of the FreeBSD Project.
  */
 
-if (!defined('PHP_VERSION_ID') || PHP_VERSION_ID < 50400) {
-    fwrite(STDERR, "PHP Parallel Lint require PHP 5.4.0 or newer." . PHP_EOL);
+if (!defined('PHP_VERSION_ID') || PHP_VERSION_ID < 50300) {
+    fwrite(STDERR, "PHP Parallel Lint requires PHP 5.3.0 or newer." . PHP_EOL);
     exit(254);
 }
 
-$autoloadLocations = [
+$autoloadLocations = array(
     getcwd() . '/vendor/autoload.php',
     getcwd() . '/../../autoload.php',
     __DIR__ . '/vendor/autoload.php',
     __DIR__ . '/../vendor/autoload.php',
     __DIR__ . '/../../../autoload.php',
     __DIR__ . '/../../autoload.php',
-];
+);
 
 $loaded = false;
 foreach ($autoloadLocations as $autoload) {
@@ -61,5 +61,7 @@ if (!$loaded) {
     exit(254);
 }
 
+require_once __DIR__ . '/src/polyfill.php';
+
 $app = new JakubOnderka\PhpParallelLint\Application();
 exit($app->run());
diff --git a/src/polyfill.php b/src/polyfill.php
new file mode 100644
index 0000000..79b3049
--- /dev/null
+++ b/src/polyfill.php
@@ -0,0 +1,15 @@
+<?php
+
+/**
+ * Polyfill for PHP < 5.4
+ */
+if (!interface_exists('JsonSerializable', false)) {
+    interface JsonSerializable
+    {
+        /**
+         * @param void
+         * @return mixed
+         */
+        function jsonSerialize();
+    }
+}