diff --git a/appveyor.yml b/appveyor.yml
index 678667ae8..80094625e 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -32,6 +32,7 @@ install:
       pip install
         tox
         pywin32
+        certifi
     )
   - if not defined TOXENV (
       pip install
@@ -44,6 +45,7 @@ install:
         slimit
         setproctitle
         pywin32
+        certifi
         pygame
         bbfreeze
         pefile
diff --git a/deluge/common.py b/deluge/common.py
index f90d58799..97d2ba441 100644
--- a/deluge/common.py
+++ b/deluge/common.py
@@ -40,6 +40,12 @@ except ImportError:
     from urlparse import urljoin  # pylint: disable=ungrouped-imports
     from urllib import pathname2url, unquote_plus  # pylint: disable=ungrouped-imports
 
+# Windows workaround for HTTPS requests requiring certificate authority bundle.
+# see: https://twistedmatrix.com/trac/ticket/9209
+if platform.system() in ('Windows', 'Microsoft'):
+    from certifi import where
+    os.environ['SSL_CERT_FILE'] = where()
+
 DBUS_FILEMAN = None
 # gi makes dbus available on Window but don't import it as unused.
 if platform.system() not in ('Windows', 'Microsoft', 'Darwin'):
diff --git a/deluge/core/core.py b/deluge/core/core.py
index 76abfc8ac..691a7c0d2 100644
--- a/deluge/core/core.py
+++ b/deluge/core/core.py
@@ -1121,23 +1121,15 @@ class Core(component.Component):
         port = self.get_listen_port()
         url = 'https://deluge-torrent.org/test_port.php?port=%s' % port
         agent = Agent(reactor, connectTimeout=30)
-        d = agent.request(
-            b'GET',
-            url.encode('utf-8'),
-        )
+        d = agent.request(b'GET', url.encode())
 
-        def on_get_page(response):
-            d = readBody(response)
-            d.addCallback(on_read_body)
-            return d
-
-        def on_read_body(body):
+        def on_get_page(body):
             return bool(int(body))
 
         def on_error(failure):
             log.warning('Error testing listen port: %s', failure)
 
-        d.addCallback(on_get_page)
+        d.addCallback(readBody).addCallback(on_get_page)
         d.addErrback(on_error)
 
         return d