diff --git a/sites/__init__.py b/sites/__init__.py
index 9a91f4f..8933b1d 100644
--- a/sites/__init__.py
+++ b/sites/__init__.py
@@ -105,7 +105,7 @@ class Site:
         if not page:
             if retry and retry > 0:
                 delay = retry_delay
-                if page.headers['Retry-After']:
+                if 'Retry-After' in page.headers:
                     delay = int(page.headers['Retry-After'])
                 logger.warning("Load failed: waiting %s to retry (%s)", delay, page)
                 time.sleep(delay)