diff --git a/changelog.d/4510.misc b/changelog.d/4510.misc
new file mode 100644
index 000000000..43f896361
--- /dev/null
+++ b/changelog.d/4510.misc
@@ -0,0 +1 @@
+Add infrastructure to support different event formats
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index 4aa04b958..668161423 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -322,7 +322,7 @@ class FederationServer(FederationBase):
             if self.hs.is_mine_id(event.event_id):
                 event.signatures.update(
                     compute_event_signature(
-                        event,
+                        event.get_pdu_json(),
                         self.hs.hostname,
                         self.hs.config.signing_key[0]
                     )
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index adf59db7a..fcaf7530b 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -1300,7 +1300,7 @@ class FederationHandler(BaseHandler):
 
         event.signatures.update(
             compute_event_signature(
-                event,
+                event.get_pdu_json(),
                 self.hs.hostname,
                 self.hs.config.signing_key[0]
             )