diff --git a/composer.json b/composer.json
index 66dae6d..a3906b2 100644
--- a/composer.json
+++ b/composer.json
@@ -18,6 +18,7 @@
     ],
     "require": {
         "php": "^7.0",
+        "ext-ctype": "*",
         "ext-intl": "*",
         "pcrov/unicode": "^0.1",
         "psr/http-message": "^1"
diff --git a/readme.md b/readme.md
index 039a9dc..d481a21 100644
--- a/readme.md
+++ b/readme.md
@@ -9,7 +9,7 @@ This is a streaming pull parser - like [XMLReader](http://php.net/xmlreader) but
 
 ## Requirements
 
-PHP 7 and the Intl extension
+PHP 7 with the Ctype and Intl extensions.
 
 ## Installation