diff --git a/swh/web/api/throttling.py b/swh/web/api/throttling.py
index f56b0917331c059ea022df6fa2c8b600c311dedf..c833759527a5807a918aed4e849451a248a9fea1 100644
--- a/swh/web/api/throttling.py
+++ b/swh/web/api/throttling.py
@@ -1,17 +1,25 @@
-# Copyright (C) 2017-2018  The Software Heritage developers
+# Copyright (C) 2017-2020  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU Affero General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
-import ipaddress
+from ipaddress import (
+    ip_address, ip_network, IPv4Network, IPv6Network
+)
+from typing import Callable, List, TypeVar, Union
 
 from django.core.exceptions import ImproperlyConfigured
+import rest_framework
 from rest_framework.throttling import ScopedRateThrottle
 import sentry_sdk
 
 from swh.web.config import get_config
 
 
+APIView = TypeVar('APIView', bound='rest_framework.views.APIView')
+Request = rest_framework.request.Request
+
+
 class SwhWebRateThrottle(ScopedRateThrottle):
     """Custom request rate limiter for DRF enabling to exempt
     specific networks specified in swh-web configuration.
@@ -54,18 +62,19 @@ class SwhWebRateThrottle(ScopedRateThrottle):
         super().__init__()
         self.exempted_networks = None
 
-    def get_exempted_networks(self, scope_name):
+    def get_exempted_networks(self, scope_name: str
+                              ) -> List[Union[IPv4Network, IPv6Network]]:
         if not self.exempted_networks:
             scopes = get_config()['throttling']['scopes']
             scope = scopes.get(scope_name)
             if scope:
                 networks = scope.get('exempted_networks')
                 if networks:
-                    self.exempted_networks = [ipaddress.ip_network(network)
+                    self.exempted_networks = [ip_network(network)
                                               for network in networks]
         return self.exempted_networks
 
-    def allow_request(self, request, view):
+    def allow_request(self, request: Request, view: APIView) -> bool:
         # class based view case
         if not self.scope:
 
@@ -74,7 +83,8 @@ class SwhWebRateThrottle(ScopedRateThrottle):
             if default_scope is not None:
                 # check if there is a specific rate limiting associated
                 # to the request type
-                request_scope = default_scope + '_' + request.method.lower()
+                assert request.method is not None
+                request_scope = f'{default_scope}_{request.method.lower()}'
                 setattr(view, self.scope_attr, request_scope)
                 try:
                     request_allowed = super().allow_request(request, view)
@@ -109,7 +119,7 @@ class SwhWebRateThrottle(ScopedRateThrottle):
         exempted_ip = False
 
         if exempted_networks:
-            remote_address = ipaddress.ip_address(self.get_ident(request))
+            remote_address = ip_address(self.get_ident(request))
             exempted_ip = any(remote_address in network
                               for network in exempted_networks)
             request_allowed = exempted_ip or request_allowed
@@ -121,12 +131,14 @@ class SwhWebRateThrottle(ScopedRateThrottle):
             hit_count = len(self.history)
             request.META['RateLimit-Limit'] = self.num_requests
             request.META['RateLimit-Remaining'] = self.num_requests - hit_count
-            request.META['RateLimit-Reset'] = int(self.now + self.wait())
+            wait = self.wait()
+            if wait is not None:
+                request.META['RateLimit-Reset'] = int(self.now + wait)
 
         return request_allowed
 
 
-def throttle_scope(scope):
+def throttle_scope(scope: str) -> Callable[..., APIView]:
     """Decorator that allows the throttle scope of a DRF
     function based view to be set::
 
@@ -136,7 +148,7 @@ def throttle_scope(scope):
             ...
 
     """
-    def decorator(func):
+    def decorator(func: APIView) -> APIView:
         SwhScopeRateThrottle = type(
             'CustomScopeRateThrottle',
             (SwhWebRateThrottle,),