diff --git a/synapse/events/builder.py b/synapse/events/builder.py
index 399775133..291fb38a2 100644
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -23,6 +23,7 @@ from synapse.api.room_versions import (
     KNOWN_EVENT_FORMAT_VERSIONS,
     KNOWN_ROOM_VERSIONS,
     EventFormatVersions,
+    RoomVersion,
 )
 from synapse.crypto.event_signing import add_hashes_and_signatures
 from synapse.types import EventID
@@ -40,7 +41,7 @@ class EventBuilder(object):
     content/unsigned/internal_metadata fields are still mutable)
 
     Attributes:
-        format_version (int): Event format version
+        room_version: Version of the target room
         room_id (str)
         type (str)
         sender (str)
@@ -63,7 +64,7 @@ class EventBuilder(object):
     _hostname = attr.ib()
     _signing_key = attr.ib()
 
-    format_version = attr.ib()
+    room_version = attr.ib(type=RoomVersion)
 
     room_id = attr.ib()
     type = attr.ib()
@@ -108,7 +109,8 @@ class EventBuilder(object):
         )
         auth_ids = yield self._auth.compute_auth_events(self, state_ids)
 
-        if self.format_version == EventFormatVersions.V1:
+        format_version = self.room_version.event_format
+        if format_version == EventFormatVersions.V1:
             auth_events = yield self._store.add_event_hashes(auth_ids)
             prev_events = yield self._store.add_event_hashes(prev_event_ids)
         else:
@@ -148,7 +150,7 @@ class EventBuilder(object):
             clock=self._clock,
             hostname=self._hostname,
             signing_key=self._signing_key,
-            format_version=self.format_version,
+            format_version=format_version,
             event_dict=event_dict,
             internal_metadata_dict=self.internal_metadata.get_dict(),
         )
@@ -201,7 +203,7 @@ class EventBuilderFactory(object):
             clock=self.clock,
             hostname=self.hostname,
             signing_key=self.signing_key,
-            format_version=room_version.event_format,
+            room_version=room_version,
             type=key_values["type"],
             state_key=key_values.get("state_key"),
             room_id=key_values["room_id"],
diff --git a/tests/handlers/test_presence.py b/tests/handlers/test_presence.py
index d4293b431..69914428e 100644
--- a/tests/handlers/test_presence.py
+++ b/tests/handlers/test_presence.py
@@ -19,7 +19,7 @@ from mock import Mock, call
 from signedjson.key import generate_signing_key
 
 from synapse.api.constants import EventTypes, Membership, PresenceState
-from synapse.events import room_version_to_event_format
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.events.builder import EventBuilder
 from synapse.handlers.presence import (
     EXTERNAL_PROCESS_EXPIRY,
@@ -597,7 +597,7 @@ class PresenceJoinTestCase(unittest.HomeserverTestCase):
             clock=self.clock,
             hostname=hostname,
             signing_key=self.random_signing_key,
-            format_version=room_version_to_event_format(room_version),
+            room_version=KNOWN_ROOM_VERSIONS[room_version],
             room_id=room_id,
             type=EventTypes.Member,
             sender=user_id,