diff --git a/sync3/avatar.go b/sync3/avatar.go
new file mode 100644
index 0000000..63e494b
--- /dev/null
+++ b/sync3/avatar.go
@@ -0,0 +1,42 @@
+package sync3
+
+import (
+	"bytes"
+	"encoding/json"
+)
+
+// An AvatarChange represents a change to a room's avatar. There are three cases:
+//   - an empty string represents no change, and should be omitted when JSON-serialised;
+//   - the sentinel `<no-avatar>` represents a room that has never had an avatar,
+//     or a room whose avatar has been removed. It is JSON-serialised as null.
+//   - All other strings represent the current avatar of the room and JSON-serialise as
+//     normal.
+type AvatarChange string
+
+const DeletedAvatar = AvatarChange("<no-avatar>")
+const UnchangedAvatar AvatarChange = ""
+
+// NewAvatarChange interprets an optional avatar string as an AvatarChange.
+func NewAvatarChange(avatar string) AvatarChange {
+	if avatar == "" {
+		return DeletedAvatar
+	}
+	return AvatarChange(avatar)
+}
+
+func (a AvatarChange) MarshalJSON() ([]byte, error) {
+	if a == DeletedAvatar {
+		return []byte(`null`), nil
+	} else {
+		return json.Marshal(string(a))
+	}
+}
+
+// Note: the unmarshalling is only used in tests.
+func (a *AvatarChange) UnmarshalJSON(data []byte) error {
+	if bytes.Equal(data, []byte("null")) {
+		*a = DeletedAvatar
+		return nil
+	}
+	return json.Unmarshal(data, (*string)(a))
+}
diff --git a/sync3/room.go b/sync3/room.go
index 6bf7c35..3e40098 100644
--- a/sync3/room.go
+++ b/sync3/room.go
@@ -10,6 +10,7 @@ import (
 
 type Room struct {
 	Name              string            `json:"name,omitempty"`
+	AvatarChange      AvatarChange      `json:"avatar,omitempty"`
 	RequiredState     []json.RawMessage `json:"required_state,omitempty"`
 	Timeline          []json.RawMessage `json:"timeline,omitempty"`
 	InviteState       []json.RawMessage `json:"invite_state,omitempty"`
diff --git a/sync3/room_test.go b/sync3/room_test.go
new file mode 100644
index 0000000..09ec058
--- /dev/null
+++ b/sync3/room_test.go
@@ -0,0 +1,74 @@
+package sync3
+
+import (
+	"encoding/json"
+	"fmt"
+	"github.com/tidwall/gjson"
+	"reflect"
+	"testing"
+)
+
+func TestAvatarChangeMarshalling(t *testing.T) {
+	var url = "mxc://..."
+	testCases := []struct {
+		Name         string
+		AvatarChange AvatarChange
+		Check        func(avatar gjson.Result) error
+	}{
+		{
+			Name:         "Avatar exists",
+			AvatarChange: NewAvatarChange(url),
+			Check: func(avatar gjson.Result) error {
+				if !(avatar.Exists() && avatar.Type == gjson.String && avatar.Str == url) {
+					return fmt.Errorf("unexpected marshalled avatar: got %#v want %s", avatar, url)
+				}
+				return nil
+			},
+		},
+		{
+			Name:         "Avatar doesn't exist",
+			AvatarChange: DeletedAvatar,
+			Check: func(avatar gjson.Result) error {
+				if !(avatar.Exists() && avatar.Type == gjson.Null) {
+					return fmt.Errorf("unexpected marshalled Avatar: got %#v want null", avatar)
+				}
+				return nil
+			},
+		},
+		{
+			Name:         "Avatar unchanged",
+			AvatarChange: UnchangedAvatar,
+			Check: func(avatar gjson.Result) error {
+				if avatar.Exists() {
+					return fmt.Errorf("unexpected marshalled Avatar: got %#v want omitted", avatar)
+				}
+				return nil
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.Name, func(t *testing.T) {
+			room := Room{AvatarChange: tc.AvatarChange}
+			marshalled, err := json.Marshal(room)
+			t.Logf("Marshalled to %s", string(marshalled))
+			if err != nil {
+				t.Fatal(err)
+			}
+			avatar := gjson.GetBytes(marshalled, "avatar")
+			if err = tc.Check(avatar); err != nil {
+				t.Fatal(err)
+			}
+
+			var unmarshalled Room
+			err = json.Unmarshal(marshalled, &unmarshalled)
+			if err != nil {
+				t.Fatal(err)
+			}
+			t.Logf("Unmarshalled to %#v", unmarshalled.AvatarChange)
+			if !reflect.DeepEqual(unmarshalled, room) {
+				t.Fatalf("Unmarshalled struct is different from original")
+			}
+		})
+	}
+}
diff --git a/testutils/m/match.go b/testutils/m/match.go
index eb852f5..f8f6c6a 100644
--- a/testutils/m/match.go
+++ b/testutils/m/match.go
@@ -39,6 +39,39 @@ func MatchRoomName(name string) RoomMatcher {
 	}
 }
 
+// MatchRoomAvatar builds a RoomMatcher which checks that the given room response has
+// set the room's avatar to the given value.
+func MatchRoomAvatar(wantAvatar string) RoomMatcher {
+	return func(r sync3.Room) error {
+		if string(r.AvatarChange) != wantAvatar {
+			return fmt.Errorf("MatchRoomAvatar: got \"%s\" want \"%s\"", r.AvatarChange, wantAvatar)
+		}
+		return nil
+	}
+}
+
+// MatchRoomUnsetAvatar builds a RoomMatcher which checks that the given room has no
+// avatar, or has had its avatar deleted.
+func MatchRoomUnsetAvatar() RoomMatcher {
+	return func(r sync3.Room) error {
+		if r.AvatarChange != sync3.DeletedAvatar {
+			return fmt.Errorf("MatchRoomAvatar: got \"%s\" want \"%s\"", r.AvatarChange, sync3.DeletedAvatar)
+		}
+		return nil
+	}
+}
+
+// MatchRoomUnchangedAvatar builds a RoomMatcher which checks that the given room has no
+// change to its avatar, or has had its avatar deleted.
+func MatchRoomUnchangedAvatar() RoomMatcher {
+	return func(r sync3.Room) error {
+		if r.AvatarChange != sync3.UnchangedAvatar {
+			return fmt.Errorf("MatchRoomAvatar: got \"%s\" want \"%s\"", r.AvatarChange, sync3.UnchangedAvatar)
+		}
+		return nil
+	}
+}
+
 func MatchJoinCount(count int) RoomMatcher {
 	return func(r sync3.Room) error {
 		if r.JoinedCount != count {