diff --git a/aiogram/utils/mixins.py b/aiogram/utils/mixins.py
index e6857263..90ef4edb 100644
--- a/aiogram/utils/mixins.py
+++ b/aiogram/utils/mixins.py
@@ -22,6 +22,9 @@ class DataMixin:
     def __delitem__(self, key):
         del self.data[key]
 
+    def __contains__(self, key):
+        return key in self.data
+
     def get(self, key, default=None):
         return self.data.get(key, default)