diff --git a/axes/middleware.py b/axes/middleware.py
index 4e7d7be..b9ace17 100644
--- a/axes/middleware.py
+++ b/axes/middleware.py
@@ -42,7 +42,9 @@ class AxesMiddleware:
     @staticmethod
     def set_retry_after_header(request: HttpRequest, response: HttpResponse) -> None:
         if settings.AXES_ENABLE_RETRY_AFTER_HEADER:
-            response["Retry-After"] = str(int(get_cool_off(request).total_seconds()))
+            cool_off = get_cool_off(request)
+            if cool_off is not None:
+                response["Retry-After"] = str(int(cool_off.total_seconds()))
 
     def build_lockout_response(
         self,
@@ -75,8 +77,6 @@ class AxesMiddleware:
                 credentials = getattr(request, "axes_credentials", None)
                 response = await sync_to_async(
                     self.build_lockout_response, thread_sensitive=True
-                )(
-                    request, response, credentials
-                )
+                )(request, response, credentials)
 
         return response
diff --git a/docs/4_configuration.rst b/docs/4_configuration.rst
index c95fbd8..e6a39c8 100644
--- a/docs/4_configuration.rst
+++ b/docs/4_configuration.rst
@@ -91,7 +91,8 @@ The following ``settings.py`` options are available for customizing Axes behavio
 +------------------------------------------------------+----------------------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
 
 .. note::
-   If ``AXES_ENABLE_RETRY_AFTER_HEADER`` is enabled and ``AXES_COOLOFF_TIME`` is configured,
+   ``AXES_ENABLE_RETRY_AFTER_HEADER`` defaults to ``False``.
+   If enabled and ``AXES_COOLOFF_TIME`` is configured,
    ``AxesMiddleware`` adds a ``Retry-After`` HTTP header (`RFC 7231 <https://datatracker.ietf.org/doc/html/rfc7231#section-7.1.3>`_)
    with the cool-off duration in seconds for lockout responses.