requests: GAE fails with v2.16.3 | error: required argument is not a float

I have just installed the requests library in my appengine app following the instructions at https://cloud.google.com/appengine/docs/standard/python/issue-requests . When making the following request (within the app or within the interactive console)

import requests
import requests_toolbelt.adapters.appengine

# Use the App Engine Requests adapter. This makes sure that Requests uses
# URLFetch.
requests_toolbelt.adapters.appengine.monkeypatch()

r = requests.get('https://api.github.com/events')

I get the following error

> Traceback (most recent call last):
>   File "/usr/local/y/google-cloud-sdk/platform/google_appengine/google/appengine/tools/devappserver2/python/request_handler.py", line 226, in handle_interactive_request
>     exec(compiled_code, self._command_globals)
>   File "<string>", line 8, in <module>
>   File "/Users/developer/Desktop/myapp-web/libraries/requests/api.py", line 72, in get
>     return request('get', url, params=params, **kwargs)
>   File "/Users/developer/Desktop/myapp-web/libraries/requests/api.py", line 58, in request
>     return session.request(method=method, url=url, **kwargs)
>   File "/Users/developer/Desktop/myapp-web/libraries/requests/sessions.py", line 523, in request
>     resp = self.send(prep, **send_kwargs)
>   File "/Users/developer/Desktop/myapp-web/libraries/requests/sessions.py", line 643, in send
>     r = adapter.send(request, **kwargs)
>   File "/Users/developer/Desktop/myapp-web/libraries/requests/adapters.py", line 440, in send
>     timeout=timeout
>   File "/Users/developer/Desktop/myapp-web/libraries/requests_toolbelt/adapters/appengine.py", line 172, in urlopen
>     **response_kw)
>   File "/Users/developer/Desktop/myapp-web/libraries/urllib3/contrib/appengine.py", line 149, in urlopen
>     validate_certificate=self.validate_certificate,
>   File "/usr/local/y/google-cloud-sdk/platform/google_appengine/google/appengine/api/urlfetch.py", line 293, in fetch
>     return rpc.get_result()
>   File "/usr/local/y/google-cloud-sdk/platform/google_appengine/google/appengine/api/apiproxy_stub_map.py", line 613, in get_result
>     return self.__get_result_hook(self)
>   File "/usr/local/y/google-cloud-sdk/platform/google_appengine/google/appengine/api/urlfetch.py", line 413, in _get_fetch_result
>     rpc.check_success()
>   File "/usr/local/y/google-cloud-sdk/platform/google_appengine/google/appengine/api/apiproxy_stub_map.py", line 579, in check_success
>     self.__rpc.CheckSuccess()
>   File "/usr/local/y/google-cloud-sdk/platform/google_appengine/google/appengine/api/apiproxy_rpc.py", line 157, in _WaitImpl
>     self.request, self.response)
>   File "/usr/local/y/google-cloud-sdk/platform/google_appengine/google/appengine/ext/remote_api/remote_api_stub.py", line 206, in MakeSyncCall
>     self._MakeRealSyncCall(service, call, request, response)
>   File "/usr/local/y/google-cloud-sdk/platform/google_appengine/google/appengine/ext/remote_api/remote_api_stub.py", line 255, in _MakeRealSyncCall
>     request_pb.set_request(request.Encode())
>   File "/usr/local/y/google-cloud-sdk/platform/google_appengine/google/net/proto/ProtocolBuffer.py", line 103, in Encode
>     self.Output(e)
>   File "/usr/local/y/google-cloud-sdk/platform/google_appengine/google/net/proto/ProtocolBuffer.py", line 347, in Output
>     self.OutputUnchecked(e)
>   File "/usr/local/y/google-cloud-sdk/platform/google_appengine/google/appengine/api/urlfetch_service_pb.py", line 484, in OutputUnchecked
>     out.putDouble(self.deadline_)
>   File "/usr/local/y/google-cloud-sdk/platform/google_appengine/google/net/proto/ProtocolBuffer.py", line 592, in putDouble
>     a.fromstring(struct.pack("<d", v))
> error: required argument is not a float

I have the following packages installed (along with dependencies) via pip

requests-2.16.3.dist-info
requests_toolbelt-0.8.0.dist-info