diff --git a/composer.json b/composer.json
index c370330..06d9b03 100644
--- a/composer.json
+++ b/composer.json
@@ -24,7 +24,7 @@
     "require-dev": {
         "phpunit/phpunit": "^7.5.13",
         "mikey179/vfsStream": "^1.6.4",
-        "slim/slim": "^3.0",
+        "slim/slim": "^3.0 || ^4.0",
         "zendframework/zend-expressive": "^3.0",
         "zendframework/zend-expressive-fastroute": "^3.0.1",
         "zendframework/zend-servicemanager": "^3.3.2",