diff --git a/syncapi/synctypes/clientevent_test.go b/syncapi/synctypes/clientevent_test.go
index 588fa2834..cd5e6a368 100644
--- a/syncapi/synctypes/clientevent_test.go
+++ b/syncapi/synctypes/clientevent_test.go
@@ -18,12 +18,16 @@ package synctypes
 import (
 	"bytes"
 	"encoding/json"
+	"reflect"
 	"testing"
 
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/gomatrixserverlib/spec"
 )
 
+const testSenderID = "testSenderID"
+const testUserID = "@test:localhost"
+
 func TestToClientEvent(t *testing.T) { // nolint: gocyclo
 	ev, err := gomatrixserverlib.MustGetRoomVersion(gomatrixserverlib.RoomVersionV1).NewEventFromTrustedJSON([]byte(`{
 		"type": "m.room.name",
@@ -114,3 +118,294 @@ func TestToClientFormatSync(t *testing.T) {
 		t.Errorf("ClientEvent.RoomID: wanted '', got %s", ce.RoomID)
 	}
 }
+
+func TestToClientEventFormatSyncFederation(t *testing.T) { // nolint: gocyclo
+	ev, err := gomatrixserverlib.MustGetRoomVersion(gomatrixserverlib.RoomVersionV10).NewEventFromTrustedJSON([]byte(`{
+		"type": "m.room.name",
+		"state_key": "",
+		"event_id": "$test:localhost",
+		"room_id": "!test:localhost",
+		"sender": "@test:localhost",
+		"content": {
+			"name": "Hello World"
+		},
+		"origin_server_ts": 123456,
+		"unsigned": {
+			"prev_content": {
+				"name": "Goodbye World"
+			}
+		},
+        "depth": 8,
+        "prev_events": [
+          "$f597Tp0Mm1PPxEgiprzJc2cZAjVhxCxACOGuwJb33Oo"
+        ],
+        "auth_events": [
+          "$Bj0ZGgX6VTqAQdqKH4ZG3l6rlbxY3rZlC5D3MeuK1OQ",
+          "$QsMs6A1PUVUhgSvmHBfpqEYJPgv4DXt96r8P2AK7iXQ",
+          "$tBteKtlnFiwlmPJsv0wkKTMEuUVWpQH89H7Xskxve1Q"
+        ]
+	}`), false)
+	if err != nil {
+		t.Fatalf("failed to create Event: %s", err)
+	}
+	userID, err := spec.NewUserID("@test:localhost", true)
+	if err != nil {
+		t.Fatalf("failed to create userID: %s", err)
+	}
+	sk := ""
+	ce := ToClientEvent(ev, FormatSyncFederation, userID.String(), &sk, ev.Unsigned())
+	if ce.EventID != ev.EventID() {
+		t.Errorf("ClientEvent.EventID: wanted %s, got %s", ev.EventID(), ce.EventID)
+	}
+	if ce.OriginServerTS != ev.OriginServerTS() {
+		t.Errorf("ClientEvent.OriginServerTS: wanted %d, got %d", ev.OriginServerTS(), ce.OriginServerTS)
+	}
+	if ce.StateKey == nil || *ce.StateKey != "" {
+		t.Errorf("ClientEvent.StateKey: wanted '', got %v", ce.StateKey)
+	}
+	if ce.Type != ev.Type() {
+		t.Errorf("ClientEvent.Type: wanted %s, got %s", ev.Type(), ce.Type)
+	}
+	if !bytes.Equal(ce.Content, ev.Content()) {
+		t.Errorf("ClientEvent.Content: wanted %s, got %s", string(ev.Content()), string(ce.Content))
+	}
+	if !bytes.Equal(ce.Unsigned, ev.Unsigned()) {
+		t.Errorf("ClientEvent.Unsigned: wanted %s, got %s", string(ev.Unsigned()), string(ce.Unsigned))
+	}
+	if ce.Sender != userID.String() {
+		t.Errorf("ClientEvent.Sender: wanted %s, got %s", userID.String(), ce.Sender)
+	}
+	if ce.Depth != ev.Depth() {
+		t.Errorf("ClientEvent.Depth: wanted %d, got %d", ev.Depth(), ce.Depth)
+	}
+	if !reflect.DeepEqual(ce.PrevEvents, ev.PrevEventIDs()) {
+		t.Errorf("ClientEvent.PrevEvents: wanted %v, got %v", ev.PrevEventIDs(), ce.PrevEvents)
+	}
+	if !reflect.DeepEqual(ce.AuthEvents, ev.AuthEventIDs()) {
+		t.Errorf("ClientEvent.AuthEvents: wanted %v, got %v", ev.AuthEventIDs(), ce.AuthEvents)
+	}
+}
+
+func userIDForSender(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+	return spec.NewUserID(testUserID, true)
+}
+
+func TestToClientEventsFormatSyncFederation(t *testing.T) { // nolint: gocyclo
+	ev, err := gomatrixserverlib.MustGetRoomVersion(gomatrixserverlib.RoomVersionPseudoIDs).NewEventFromTrustedJSON([]byte(`{
+		"type": "m.room.name",
+        "state_key": "testSenderID",
+		"event_id": "$test:localhost",
+		"room_id": "!test:localhost",
+		"sender": "testSenderID",
+		"content": {
+			"name": "Hello World"
+		},
+		"origin_server_ts": 123456,
+		"unsigned": {
+			"prev_content": {
+				"name": "Goodbye World"
+			}
+		},
+        "depth": 8,
+        "prev_events": [
+          "$f597Tp0Mm1PPxEgiprzJc2cZAjVhxCxACOGuwJb33Oo"
+        ],
+        "auth_events": [
+          "$Bj0ZGgX6VTqAQdqKH4ZG3l6rlbxY3rZlC5D3MeuK1OQ",
+          "$QsMs6A1PUVUhgSvmHBfpqEYJPgv4DXt96r8P2AK7iXQ",
+          "$tBteKtlnFiwlmPJsv0wkKTMEuUVWpQH89H7Xskxve1Q"
+        ]
+	}`), false)
+	if err != nil {
+		t.Fatalf("failed to create Event: %s", err)
+	}
+	ev2, err := gomatrixserverlib.MustGetRoomVersion(gomatrixserverlib.RoomVersionPseudoIDs).NewEventFromTrustedJSON([]byte(`{
+		"type": "m.room.name",
+        "state_key": "testSenderID",
+		"event_id": "$test2:localhost",
+		"room_id": "!test:localhost",
+		"sender": "testSenderID",
+		"content": {
+			"name": "Hello World 2"
+		},
+		"origin_server_ts": 1234567,
+		"unsigned": {
+			"prev_content": {
+				"name": "Goodbye World 2"
+			},
+            "prev_sender": "testSenderID"
+		},
+        "depth": 9,
+        "prev_events": [
+          "$f597Tp0Mm1PPxEgiprzJc2cZAjVhxCxACOGuwJb33Oo"
+        ],
+        "auth_events": [
+          "$Bj0ZGgX6VTqAQdqKH4ZG3l6rlbxY3rZlC5D3MeuK1OQ",
+          "$QsMs6A1PUVUhgSvmHBfpqEYJPgv4DXt96r8P2AK7iXQ",
+          "$tBteKtlnFiwlmPJsv0wkKTMEuUVWpQH89H7Xskxve1Q"
+        ]
+    }`), false)
+	if err != nil {
+		t.Fatalf("failed to create Event: %s", err)
+	}
+
+	clientEvents := ToClientEvents([]gomatrixserverlib.PDU{ev, ev2}, FormatSyncFederation, userIDForSender)
+	ce := clientEvents[0]
+	if ce.EventID != ev.EventID() {
+		t.Errorf("ClientEvent.EventID: wanted %s, got %s", ev.EventID(), ce.EventID)
+	}
+	if ce.OriginServerTS != ev.OriginServerTS() {
+		t.Errorf("ClientEvent.OriginServerTS: wanted %d, got %d", ev.OriginServerTS(), ce.OriginServerTS)
+	}
+	if ce.StateKey == nil || *ce.StateKey != testSenderID {
+		t.Errorf("ClientEvent.StateKey: wanted %s, got %v", testSenderID, ce.StateKey)
+	}
+	if ce.Type != ev.Type() {
+		t.Errorf("ClientEvent.Type: wanted %s, got %s", ev.Type(), ce.Type)
+	}
+	if !bytes.Equal(ce.Content, ev.Content()) {
+		t.Errorf("ClientEvent.Content: wanted %s, got %s", string(ev.Content()), string(ce.Content))
+	}
+	if !bytes.Equal(ce.Unsigned, ev.Unsigned()) {
+		t.Errorf("ClientEvent.Unsigned: wanted %s, got %s", string(ev.Unsigned()), string(ce.Unsigned))
+	}
+	if ce.Sender != testSenderID {
+		t.Errorf("ClientEvent.Sender: wanted %s, got %s", testSenderID, ce.Sender)
+	}
+	if ce.Depth != ev.Depth() {
+		t.Errorf("ClientEvent.Depth: wanted %d, got %d", ev.Depth(), ce.Depth)
+	}
+	if !reflect.DeepEqual(ce.PrevEvents, ev.PrevEventIDs()) {
+		t.Errorf("ClientEvent.PrevEvents: wanted %v, got %v", ev.PrevEventIDs(), ce.PrevEvents)
+	}
+	if !reflect.DeepEqual(ce.AuthEvents, ev.AuthEventIDs()) {
+		t.Errorf("ClientEvent.AuthEvents: wanted %v, got %v", ev.AuthEventIDs(), ce.AuthEvents)
+	}
+
+	ce2 := clientEvents[1]
+	if ce2.EventID != ev2.EventID() {
+		t.Errorf("ClientEvent.EventID: wanted %s, got %s", ev2.EventID(), ce2.EventID)
+	}
+	if ce2.OriginServerTS != ev2.OriginServerTS() {
+		t.Errorf("ClientEvent.OriginServerTS: wanted %d, got %d", ev2.OriginServerTS(), ce2.OriginServerTS)
+	}
+	if ce2.StateKey == nil || *ce.StateKey != testSenderID {
+		t.Errorf("ClientEvent.StateKey: wanted %s, got %v", testSenderID, ce2.StateKey)
+	}
+	if ce2.Type != ev2.Type() {
+		t.Errorf("ClientEvent.Type: wanted %s, got %s", ev2.Type(), ce2.Type)
+	}
+	if !bytes.Equal(ce2.Content, ev2.Content()) {
+		t.Errorf("ClientEvent.Content: wanted %s, got %s", string(ev2.Content()), string(ce2.Content))
+	}
+	if !bytes.Equal(ce2.Unsigned, ev2.Unsigned()) {
+		t.Errorf("ClientEvent.Unsigned: wanted %s, got %s", string(ev2.Unsigned()), string(ce2.Unsigned))
+	}
+	if ce2.Sender != testSenderID {
+		t.Errorf("ClientEvent.Sender: wanted %s, got %s", testSenderID, ce2.Sender)
+	}
+	if ce2.Depth != ev2.Depth() {
+		t.Errorf("ClientEvent.Depth: wanted %d, got %d", ev2.Depth(), ce2.Depth)
+	}
+	if !reflect.DeepEqual(ce2.PrevEvents, ev2.PrevEventIDs()) {
+		t.Errorf("ClientEvent.PrevEvents: wanted %v, got %v", ev2.PrevEventIDs(), ce2.PrevEvents)
+	}
+	if !reflect.DeepEqual(ce2.AuthEvents, ev2.AuthEventIDs()) {
+		t.Errorf("ClientEvent.AuthEvents: wanted %v, got %v", ev2.AuthEventIDs(), ce2.AuthEvents)
+	}
+}
+
+func TestToClientEventsFormatSync(t *testing.T) { // nolint: gocyclo
+	ev, err := gomatrixserverlib.MustGetRoomVersion(gomatrixserverlib.RoomVersionPseudoIDs).NewEventFromTrustedJSON([]byte(`{
+		"type": "m.room.name",
+        "state_key": "testSenderID",
+		"event_id": "$test:localhost",
+		"room_id": "!test:localhost",
+		"sender": "testSenderID",
+		"content": {
+			"name": "Hello World"
+		},
+		"origin_server_ts": 123456,
+		"unsigned": {
+			"prev_content": {
+				"name": "Goodbye World"
+			}
+		}
+    }`), false)
+	if err != nil {
+		t.Fatalf("failed to create Event: %s", err)
+	}
+	ev2, err := gomatrixserverlib.MustGetRoomVersion(gomatrixserverlib.RoomVersionPseudoIDs).NewEventFromTrustedJSON([]byte(`{
+		"type": "m.room.name",
+        "state_key": "testSenderID",
+		"event_id": "$test2:localhost",
+		"room_id": "!test:localhost",
+		"sender": "testSenderID",
+		"content": {
+			"name": "Hello World 2"
+		},
+		"origin_server_ts": 1234567,
+		"unsigned": {
+			"prev_content": {
+				"name": "Goodbye World 2"
+			},
+            "prev_sender": "testSenderID"
+		},
+        "depth": 9	
+    }`), false)
+	if err != nil {
+		t.Fatalf("failed to create Event: %s", err)
+	}
+
+	clientEvents := ToClientEvents([]gomatrixserverlib.PDU{ev, ev2}, FormatSync, userIDForSender)
+	ce := clientEvents[0]
+	if ce.EventID != ev.EventID() {
+		t.Errorf("ClientEvent.EventID: wanted %s, got %s", ev.EventID(), ce.EventID)
+	}
+	if ce.OriginServerTS != ev.OriginServerTS() {
+		t.Errorf("ClientEvent.OriginServerTS: wanted %d, got %d", ev.OriginServerTS(), ce.OriginServerTS)
+	}
+	if ce.StateKey == nil || *ce.StateKey != testUserID {
+		t.Errorf("ClientEvent.StateKey: wanted %s, got %v", testUserID, ce.StateKey)
+	}
+	if ce.Type != ev.Type() {
+		t.Errorf("ClientEvent.Type: wanted %s, got %s", ev.Type(), ce.Type)
+	}
+	if !bytes.Equal(ce.Content, ev.Content()) {
+		t.Errorf("ClientEvent.Content: wanted %s, got %s", string(ev.Content()), string(ce.Content))
+	}
+	if !bytes.Equal(ce.Unsigned, ev.Unsigned()) {
+		t.Errorf("ClientEvent.Unsigned: wanted %s, got %s", string(ev.Unsigned()), string(ce.Unsigned))
+	}
+	if ce.Sender != testUserID {
+		t.Errorf("ClientEvent.Sender: wanted %s, got %s", testUserID, ce.Sender)
+	}
+
+	var prev PrevEventRef
+	prev.PrevContent = []byte(`{"name": "Goodbye World 2"}`)
+	prev.PrevSenderID = testUserID
+	expectedUnsigned, _ := json.Marshal(prev)
+
+	ce2 := clientEvents[1]
+	if ce2.EventID != ev2.EventID() {
+		t.Errorf("ClientEvent.EventID: wanted %s, got %s", ev2.EventID(), ce2.EventID)
+	}
+	if ce2.OriginServerTS != ev2.OriginServerTS() {
+		t.Errorf("ClientEvent.OriginServerTS: wanted %d, got %d", ev2.OriginServerTS(), ce2.OriginServerTS)
+	}
+	if ce2.StateKey == nil || *ce.StateKey != testUserID {
+		t.Errorf("ClientEvent.StateKey: wanted %s, got %v", testUserID, ce2.StateKey)
+	}
+	if ce2.Type != ev2.Type() {
+		t.Errorf("ClientEvent.Type: wanted %s, got %s", ev2.Type(), ce2.Type)
+	}
+	if !bytes.Equal(ce2.Content, ev2.Content()) {
+		t.Errorf("ClientEvent.Content: wanted %s, got %s", string(ev2.Content()), string(ce2.Content))
+	}
+	if !bytes.Equal(ce2.Unsigned, expectedUnsigned) {
+		t.Errorf("ClientEvent.Unsigned: wanted %s, got %s", string(expectedUnsigned), string(ce2.Unsigned))
+	}
+	if ce2.Sender != testUserID {
+		t.Errorf("ClientEvent.Sender: wanted %s, got %s", testUserID, ce2.Sender)
+	}
+}