diff --git a/README.md b/README.md
index a3a34836..c93afa7a 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,10 @@ Features:
 
 This version of carddav2fb is a forked version from carlos22 (https://github.com/carlos22/carddav2fb) with certain updates applied which had been published at http://www.ip-phone-forum.de/showthread.php?t=267477. In addition to being compatible to newer FRITZ!OS versions it also features a bunch of bug fixes.
 
+## Requirements
+
+PHP version 5.3.6 or higher is required.
+
 ## Installation
 
  Checkout the carddav2fb sources including its related subprojects using the following command:
diff --git a/carddav2fb.php b/carddav2fb.php
index 7aa79aa0..3231d900 100644
--- a/carddav2fb.php
+++ b/carddav2fb.php
@@ -23,6 +23,13 @@
 error_reporting(E_ALL);
 setlocale(LC_ALL, 'de_DE.UTF8');
 
+$php_min_version = '5.3.6';
+
+if (version_compare(PHP_VERSION, $php_min_version) < 0) {
+  print 'ERROR: PHP version '.$php_min_version.' is required. Found version: ' . PHP_VERSION . PHP_EOL;
+  exit(1);
+}
+
 require_once('lib/CardDAV-PHP/carddav.php');
 require_once('lib/vCard-parser/vCard.php');
 require_once('lib/fritzbox_api_php/fritzbox_api.class.php');