diff --git a/aiogram/dispatcher/webhook.py b/aiogram/dispatcher/webhook.py
index 83c5fb74..c9e39a4f 100644
--- a/aiogram/dispatcher/webhook.py
+++ b/aiogram/dispatcher/webhook.py
@@ -132,7 +132,7 @@ class WebhookRequestHandler(web.View):
         else:
             web_response = web.Response(text='ok')
 
-        if self.request.app['RETRY_AFTER']:
+        if self.request.app.get('RETRY_AFTER', None):
             web_response.headers['Retry-After'] = self.request.app['RETRY_AFTER']
 
         return web_response