diff --git a/composer.json b/composer.json
index 268a439..f955cae 100644
--- a/composer.json
+++ b/composer.json
@@ -13,7 +13,7 @@
         "psr/log": "^1.0",
         "mtdowling/cron-expression": "^1.2",
         "malkusch/lock": "^1.0",
-        "cocur/slugify": "^2.5",
+        "cocur/slugify": ">=2.5 <4.0",
         "phossa2/event": "^2.1.0"
     },
     "require-dev": {