diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 85fdf94d0..e79a82cfc 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -125,60 +125,72 @@ class FederationHandler(BaseHandler):
         )
         if not is_in_room and not event.internal_metadata.is_outlier():
             logger.debug("Got event for room we're not in.")
-            current_state = state
 
-        event_ids = set()
-        if state:
-            event_ids |= {e.event_id for e in state}
-        if auth_chain:
-            event_ids |= {e.event_id for e in auth_chain}
+            try:
+                event_stream_id, max_stream_id = yield self._persist_auth_tree(
+                    auth_chain, state, event
+                )
+            except AuthError as e:
+                raise FederationError(
+                    "ERROR",
+                    e.code,
+                    e.msg,
+                    affected=event.event_id,
+                )
 
-        seen_ids = set(
-            (yield self.store.have_events(event_ids)).keys()
-        )
+        else:
+            event_ids = set()
+            if state:
+                event_ids |= {e.event_id for e in state}
+            if auth_chain:
+                event_ids |= {e.event_id for e in auth_chain}
 
-        if state and auth_chain is not None:
-            # If we have any state or auth_chain given to us by the replication
-            # layer, then we should handle them (if we haven't before.)
-
-            event_infos = []
-
-            for e in itertools.chain(auth_chain, state):
-                if e.event_id in seen_ids:
-                    continue
-                e.internal_metadata.outlier = True
-                auth_ids = [e_id for e_id, _ in e.auth_events]
-                auth = {
-                    (e.type, e.state_key): e for e in auth_chain
-                    if e.event_id in auth_ids
-                }
-                event_infos.append({
-                    "event": e,
-                    "auth_events": auth,
-                })
-                seen_ids.add(e.event_id)
-
-            yield self._handle_new_events(
-                origin,
-                event_infos,
-                outliers=True
+            seen_ids = set(
+                (yield self.store.have_events(event_ids)).keys()
             )
 
-        try:
-            _, event_stream_id, max_stream_id = yield self._handle_new_event(
-                origin,
-                event,
-                state=state,
-                backfilled=backfilled,
-                current_state=current_state,
-            )
-        except AuthError as e:
-            raise FederationError(
-                "ERROR",
-                e.code,
-                e.msg,
-                affected=event.event_id,
-            )
+            if state and auth_chain is not None:
+                # If we have any state or auth_chain given to us by the replication
+                # layer, then we should handle them (if we haven't before.)
+
+                event_infos = []
+
+                for e in itertools.chain(auth_chain, state):
+                    if e.event_id in seen_ids:
+                        continue
+                    e.internal_metadata.outlier = True
+                    auth_ids = [e_id for e_id, _ in e.auth_events]
+                    auth = {
+                        (e.type, e.state_key): e for e in auth_chain
+                        if e.event_id in auth_ids
+                    }
+                    event_infos.append({
+                        "event": e,
+                        "auth_events": auth,
+                    })
+                    seen_ids.add(e.event_id)
+
+                yield self._handle_new_events(
+                    origin,
+                    event_infos,
+                    outliers=True
+                )
+
+            try:
+                _, event_stream_id, max_stream_id = yield self._handle_new_event(
+                    origin,
+                    event,
+                    state=state,
+                    backfilled=backfilled,
+                    current_state=current_state,
+                )
+            except AuthError as e:
+                raise FederationError(
+                    "ERROR",
+                    e.code,
+                    e.msg,
+                    affected=event.event_id,
+                )
 
         # if we're receiving valid events from an origin,
         # it's probably a good idea to mark it as not in retry-state