diff --git a/sync2/poller.go b/sync2/poller.go
index 6592cb0..9c5facf 100644
--- a/sync2/poller.go
+++ b/sync2/poller.go
@@ -339,6 +339,8 @@ func (p *Poller) FallbackKeyTypes() []string {
 func (p *Poller) DeviceListChanges() (changed, left []string) {
 	p.e2eeMu.Lock()
 	defer p.e2eeMu.Unlock()
+	changed = make([]string, 0)
+	left = make([]string, 0)
 	for userID, state := range p.deviceListChanges {
 		switch state {
 		case "changed":
diff --git a/sync3/extensions/account_data.go b/sync3/extensions/account_data.go
index ae4bea3..5c22619 100644
--- a/sync3/extensions/account_data.go
+++ b/sync3/extensions/account_data.go
@@ -19,8 +19,8 @@ func (r AccountDataRequest) ApplyDelta(next *AccountDataRequest) *AccountDataReq
 
 // Server response
 type AccountDataResponse struct {
-	Global []json.RawMessage            `json:"global"`
-	Rooms  map[string][]json.RawMessage `json:"rooms"`
+	Global []json.RawMessage            `json:"global,omitempty"`
+	Rooms  map[string][]json.RawMessage `json:"rooms,omitempty"`
 }
 
 func (r *AccountDataResponse) HasData(isInitial bool) bool {