diff --git a/sygnal/gcmpushkin.py b/sygnal/gcmpushkin.py
index 621c2fd7..4b6b7b7b 100644
--- a/sygnal/gcmpushkin.py
+++ b/sygnal/gcmpushkin.py
@@ -14,14 +14,17 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import aiohttp
+import asyncio
 import json
 import logging
+import os
 import time
 from enum import Enum
 from io import BytesIO
 from typing import TYPE_CHECKING, Any, AnyStr, Dict, List, Optional, Tuple
 
-import google.auth.transport.requests
+import google.auth.transport._aiohttp_requests
 from google.oauth2 import service_account
 from opentracing import Span, logs, tags
 from prometheus_client import Counter, Gauge, Histogram
@@ -195,6 +198,15 @@ def __init__(self, name: str, sygnal: "Sygnal", config: Dict[str, Any]) -> None:
                 "Config field fcm_options, if set, must be a dictionary of options"
             )
 
+        self._loop = asyncio.get_event_loop()
+        self._refresh_lock = asyncio.Lock()
+        self._session = None
+
+        if proxy_url:
+            os.environ["HTTP_PROXY"] = proxy_url
+            os.environ["HTTPS_PROXY"] = proxy_url
+            self._session = aiohttp.ClientSession(trust_env=True)
+
     @classmethod
     async def create(
         cls, name: str, sygnal: "Sygnal", config: Dict[str, Any]
@@ -464,7 +476,7 @@ def _handle_v1_response(
                 f"Unknown GCM response code {response.code}"
             )
 
-    def _get_access_token(self) -> str:
+    async def _get_access_token(self) -> str:
         """Retrieve a valid access token that can be used to authorize requests.
 
         :return: Access token.
@@ -476,8 +488,12 @@ def _get_access_token(self) -> str:
             str(self.service_account_file),
             scopes=AUTH_SCOPES,
         )
-        request = google.auth.transport.requests.Request()
-        credentials.refresh(request)
+        request = google.auth.transport._aiohttp_requests.Request(session=self._session)
+        # This code is copied from https://github.com/googleapis/google-auth-library-python/blob/8cfc91db0861bc92374d708140656fb38e003ef6/google/auth/transport/_aiohttp_requests.py#L372
+        async with self._refresh_lock:
+            await self._loop.run_in_executor(
+                None, credentials.refresh, request
+            )
         return credentials.token
 
     async def _dispatch_notification_unlimited(