diff --git a/composer.json b/composer.json
index b47a68e..d347b6b 100644
--- a/composer.json
+++ b/composer.json
@@ -14,7 +14,8 @@
     ],
     "license": "MIT",
     "require": {
-        "php": "^7.1|^8.0"
+        "php": "^7.1|^8.0",
+        "ext-json": "*"
     },
     "require-dev": {
         "phpunit/phpunit": "^7.5.15|^8.5",