diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 8fa726759..f4adcb556 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -32,6 +32,7 @@ from synapse.api.errors import (
     HttpResponseException,
     SynapseError,
 )
+from synapse.crypto.event_signing import add_hashes_and_signatures
 from synapse.federation.federation_base import FederationBase, event_from_pdu_json
 from synapse.util import logcontext, unwrapFirstError
 from synapse.util.caches.expiringcache import ExpiringCache
@@ -577,7 +578,13 @@ class FederationClient(FederationBase):
             pdu_dict.pop("origin_server_ts", None)
             pdu_dict.pop("unsigned", None)
 
-            ev = self.event_builder_factory.new(pdu_dict)
+            builder = self.event_builder_factory.new(pdu_dict)
+            add_hashes_and_signatures(
+                builder,
+                self.hs.hostname,
+                self.hs.config.signing_key[0]
+            )
+            ev = builder.build()
 
             defer.returnValue(
                 (destination, ev)
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 70be87cd3..9a14ba451 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -43,7 +43,6 @@ from synapse.api.errors import (
     StoreError,
     SynapseError,
 )
-from synapse.crypto.event_signing import compute_event_signature
 from synapse.events.validator import EventValidator
 from synapse.replication.http.federation import (
     ReplicationCleanRoomRestServlet,
@@ -1079,7 +1078,6 @@ class FederationHandler(BaseHandler):
         handled_events = set()
 
         try:
-            self._sign_event(event)
             event.internal_metadata.outlier = False
 
             # Try the host we successfully got a response to /make_join/
@@ -1287,8 +1285,6 @@ class FederationHandler(BaseHandler):
         event.internal_metadata.outlier = True
         event.internal_metadata.invite_from_remote = True
 
-        self._sign_event(event)
-
         context = yield self.state_handler.compute_event_context(event)
         yield self.persist_events_and_notify([(event, context)])
 
@@ -1305,7 +1301,6 @@ class FederationHandler(BaseHandler):
         # Mark as outlier as we don't have any state for this event; we're not
         # even in the room.
         event.internal_metadata.outlier = True
-        self._sign_event(event)
 
         # Try the host that we succesfully called /make_leave/ on first for
         # the /send_leave/ request.
@@ -1349,15 +1344,6 @@ class FederationHandler(BaseHandler):
         assert(event.room_id == room_id)
         defer.returnValue((origin, event))
 
-    def _sign_event(self, event):
-        event.signatures.update(
-            compute_event_signature(
-                event,
-                self.hs.hostname,
-                self.hs.config.signing_key[0]
-            )
-        )
-
     @defer.inlineCallbacks
     @log_function
     def on_make_leave_request(self, room_id, user_id):