diff --git a/changelog.d/4033.bugfix b/changelog.d/4033.bugfix
new file mode 100644
index 000000000..4e9e38cdc
--- /dev/null
+++ b/changelog.d/4033.bugfix
@@ -0,0 +1,2 @@
+Synapse now starts on Python 3.7.
+_All_ workers now start on Python 3.
diff --git a/synapse/app/frontend_proxy.py b/synapse/app/frontend_proxy.py
index fc4b25de1..f5c61dec5 100644
--- a/synapse/app/frontend_proxy.py
+++ b/synapse/app/frontend_proxy.py
@@ -68,7 +68,7 @@ class PresenceStatusStubServlet(ClientV1RestServlet):
             "Authorization": auth_headers,
         }
         result = yield self.http_client.get_json(
-            self.main_uri + request.uri,
+            self.main_uri + request.uri.decode('ascii'),
             headers=headers,
         )
         defer.returnValue((200, result))
@@ -125,7 +125,7 @@ class KeyUploadServlet(RestServlet):
                 "Authorization": auth_headers,
             }
             result = yield self.http_client.post_json_get_json(
-                self.main_uri + request.uri,
+                self.main_uri + request.uri.decode('ascii'),
                 body,
                 headers=headers,
             )
diff --git a/synapse/visibility.py b/synapse/visibility.py
index c64ad2144..43f48196b 100644
--- a/synapse/visibility.py
+++ b/synapse/visibility.py
@@ -219,7 +219,7 @@ def filter_events_for_server(store, server_name, events):
     # Whatever else we do, we need to check for senders which have requested
     # erasure of their data.
     erased_senders = yield store.are_users_erased(
-        e.sender for e in events,
+        (e.sender for e in events),
     )
 
     def redact_disallowed(event, state):