diff --git a/composer.json b/composer.json
index affe8e0..0030da9 100644
--- a/composer.json
+++ b/composer.json
@@ -11,7 +11,9 @@
             "email": "acurrieclark@gmail.com"
         }
     ],
-    "require": {},
+    "require": {
+        "php": "^5.4.0 || ^7.0"
+    },
     "autoload": {
         "psr-4": {
             "acurrieclark\\PhpPasswordVerifier\\": "src"