diff --git a/endpoints/api/__init__.py b/endpoints/api/__init__.py
index 3e02e923f..60b5d7398 100644
--- a/endpoints/api/__init__.py
+++ b/endpoints/api/__init__.py
@@ -96,6 +96,8 @@ def truthy_bool(param):
 
 def format_date(date):
   """ Output an RFC822 date format. """
+  if date is None:
+    return None
   return formatdate(timegm(date.utctimetuple()))