diff --git a/README.md b/README.md
index 59637e8..80ceedb 100644
--- a/README.md
+++ b/README.md
@@ -16,6 +16,10 @@ for custom memory measurements.
   * Log: Timing information of current request, time spent in action controller and custom timers. Also average, min and max time for requests.
   * Variables: View variables, request info and contents of `$_COOKIE`, `$_POST` and `$_SESSION`
 
+System Requirements
+------------
+Zfdebug runs on any version of PHP between 5.3 and 8.1! (see composer.json)
+
 Installation & Usage
 ------------
 To install, place the folder 'ZFDebug' in your library path, next to the Zend
@@ -78,4 +82,4 @@ Options
 
     ; Include file list filtered
     zfdebug.plugins.File.base_path = APPLICATION_PATH "/../"
-    zfdebug.plugins.File.library = Regnskab
\ No newline at end of file
+    zfdebug.plugins.File.library = Regnskab
diff --git a/composer.json b/composer.json
index 4a1d826..568d779 100644
--- a/composer.json
+++ b/composer.json
@@ -13,6 +13,7 @@
         "library/"
     ],
     "require": {
+        "php": ">=5.3",
         "zendframework/zendframework1": "1.*"
     },
     "authors": [