diff --git a/README.md b/README.md
index 0b801e8e..e12199db 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,7 @@ Initially released in December 2012, the PHP IMAP Mailbox is a powerful and open
 * PHP `iconv` extension must be present; so make sure this line is active in your php.ini: `extension=php_iconv.dll`
 * PHP `imap` extension must be present; so make sure this line is active in your php.ini: `extension=php_imap.dll`
 * PHP `mbstring` extension must be present; so make sure this line is active in your php.ini: `extension=php_mbstring.dll`
+* PHP `json` extension must be present; so make sure this line is active in your php.ini: `extension=json.dll`
 
 ### Installation by Composer
 
diff --git a/composer.json b/composer.json
index 5e897814..77176bdd 100644
--- a/composer.json
+++ b/composer.json
@@ -27,7 +27,8 @@
         "ext-fileinfo": "*",
         "ext-iconv": "*",
         "ext-imap": "*",
-        "ext-mbstring": "*"
+        "ext-mbstring": "*",
+        "ext-json": "*"
     },
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^3.4",