diff --git a/src/github.com/matrix-org/dendrite/roomserver/api/input.go b/src/github.com/matrix-org/dendrite/roomserver/api/input.go
index fd177b19..ad32286a 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/api/input.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/api/input.go
@@ -1,6 +1,10 @@
 // Package api provides the types that are used to communicate with the roomserver.
 package api
 
+import (
+	"encoding/json"
+)
+
 const (
 	// KindOutlier event fall outside the contiguous event graph.
 	// We do not have the state for these events.
@@ -36,7 +40,61 @@ type InputRoomEvent struct {
 	// For example many matrix events forget to reference the m.room.create event even though it is needed for auth.
 	// (since synapse allows this to happen we have to allow it as well.)
 	AuthEventIDs []string
+	// Whether the state is supplied as a list of event IDs or whether it
+	// should be derived from the state at the previous events.
+	HasState bool
 	// Optional list of state event IDs forming the state before this event.
 	// These state events must have already been persisted.
+	// These are only used if HasState is true.
+	// The list can be empty, for example when storing the first event in a room.
 	StateEventIDs []string
 }
+
+// UnmarshalJSON implements json.Unmarshaller
+func (ire *InputRoomEvent) UnmarshalJSON(data []byte) error {
+	// Create a struct rather than unmarshalling directly into the InputRoomEvent
+	// so that we can use json.RawMessage.
+	// We use json.RawMessage so that the event JSON is sent as JSON rather than
+	// being base64 encoded which is the default for []byte.
+	var content struct {
+		Kind          int
+		Event         *json.RawMessage
+		AuthEventIDs  []string
+		StateEventIDs []string
+		HasState      bool
+	}
+	if err := json.Unmarshal(data, &content); err != nil {
+		return err
+	}
+	ire.Kind = content.Kind
+	ire.AuthEventIDs = content.AuthEventIDs
+	ire.StateEventIDs = content.StateEventIDs
+	ire.HasState = content.HasState
+	if content.Event != nil {
+		ire.Event = []byte(*content.Event)
+	}
+	return nil
+}
+
+// MarshalJSON implements json.Marshaller
+func (ire InputRoomEvent) MarshalJSON() ([]byte, error) {
+	// Create a struct rather than marshalling directly from the InputRoomEvent
+	// so that we can use json.RawMessage.
+	// We use json.RawMessage so that the event JSON is sent as JSON rather than
+	// being base64 encoded which is the default for []byte.
+	event := json.RawMessage(ire.Event)
+	content := struct {
+		Kind          int
+		Event         *json.RawMessage
+		AuthEventIDs  []string
+		StateEventIDs []string
+		HasState      bool
+	}{
+		Kind:          ire.Kind,
+		AuthEventIDs:  ire.AuthEventIDs,
+		StateEventIDs: ire.StateEventIDs,
+		Event:         &event,
+		HasState:      ire.HasState,
+	}
+	return json.Marshal(&content)
+}
diff --git a/src/github.com/matrix-org/dendrite/roomserver/input/events.go b/src/github.com/matrix-org/dendrite/roomserver/input/events.go
index e146d573..91999916 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/input/events.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/input/events.go
@@ -69,7 +69,7 @@ func processRoomEvent(db RoomEventDatabase, input api.InputRoomEvent) error {
 	if stateAtEvent.BeforeStateSnapshotNID == 0 {
 		// We haven't calculated a state for this event yet.
 		// Lets calculate one.
-		if input.StateEventIDs != nil {
+		if input.HasState {
 			// We've been told what the state at the event is so we don't need to calculate it.
 			// Check that those state events are in the database and store the state.
 			entries, err := db.StateEntriesForEventIDs(input.StateEventIDs)
@@ -89,6 +89,11 @@ func processRoomEvent(db RoomEventDatabase, input api.InputRoomEvent) error {
 		db.SetState(stateAtEvent.EventNID, stateAtEvent.BeforeStateSnapshotNID)
 	}
 
+	if input.Kind == api.KindBackfill {
+		// Backfill is not implemented.
+		panic("Not implemented")
+	}
+
 	// Update the extremities of the event graph for the room
 	if err := updateLatestEvents(db, roomNID, stateAtEvent, event); err != nil {
 		return err
@@ -102,5 +107,5 @@ func processRoomEvent(db RoomEventDatabase, input api.InputRoomEvent) error {
 	//      - The event itself
 	//      - The visiblity of the event, i.e. who is allowed to see the event.
 	//      - The changes to the current state of the room.
-	panic("Not implemented")
+	return nil
 }