diff --git a/sync2/handler2/handler.go b/sync2/handler2/handler.go
index 792437b..dd03ab4 100644
--- a/sync2/handler2/handler.go
+++ b/sync2/handler2/handler.go
@@ -274,6 +274,7 @@ func (h *Handler) Accumulate(ctx context.Context, userID, deviceID, roomID strin
 	for i := range timeline.Events {
 		// Delete MSC4115 field as it isn't accurate when we reuse the same event for >1 user
 		timeline.Events[i], _ = sjson.DeleteBytes(timeline.Events[i], "unsigned.membership")
+		timeline.Events[i], _ = sjson.DeleteBytes(timeline.Events[i], `unsigned.io\.element\.msc4115\.membership`)
 		parsed := gjson.ParseBytes(timeline.Events[i])
 		eventID := parsed.Get("event_id").Str
 
@@ -376,6 +377,7 @@ func (h *Handler) Accumulate(ctx context.Context, userID, deviceID, roomID strin
 func (h *Handler) Initialise(ctx context.Context, roomID string, state []json.RawMessage) error {
 	for i := range state { // Delete MSC4115 field as it isn't accurate when we reuse the same event for >1 user
 		state[i], _ = sjson.DeleteBytes(state[i], "unsigned.membership")
+		state[i], _ = sjson.DeleteBytes(state[i], `unsigned.io\.element\.msc4115\.membership`)
 	}
 	res, err := h.Store.Initialise(roomID, state)
 	if err != nil {
diff --git a/tests-integration/lists_test.go b/tests-integration/lists_test.go
index 32562bc..c0ceae9 100644
--- a/tests-integration/lists_test.go
+++ b/tests-integration/lists_test.go
@@ -2,6 +2,7 @@ package syncv3
 
 import (
 	"encoding/json"
+	"strings"
 	"testing"
 	"time"
 
@@ -364,6 +365,15 @@ func TestBumpEventTypesOnStartup(t *testing.T) {
 }
 
 func TestDeleteMSC4115Field(t *testing.T) {
+	t.Run("stable prefix", func(t *testing.T) {
+		testDeleteMSC4115Field(t, "membership")
+	})
+	t.Run("unstable prefix", func(t *testing.T) {
+		testDeleteMSC4115Field(t, "io.element.msc4115.membership")
+	})
+}
+
+func testDeleteMSC4115Field(t *testing.T, fieldName string) {
 	rig := NewTestRig(t)
 	defer rig.Finish()
 	roomID := "!TestDeleteMSC4115Field:localhost"
@@ -390,11 +400,11 @@ func TestDeleteMSC4115Field(t *testing.T) {
 
 	// ensure live events remove the field.
 	liveEvent := testutils.NewMessageEvent(t, alice, "live event", testutils.WithUnsigned(map[string]interface{}{
-		"membership": "join",
+		fieldName: "join",
 	}))
 	liveEventWithoutMembership := make(json.RawMessage, len(liveEvent))
 	copy(liveEventWithoutMembership, liveEvent)
-	liveEventWithoutMembership, err := sjson.DeleteBytes(liveEventWithoutMembership, "unsigned.membership")
+	liveEventWithoutMembership, err := sjson.DeleteBytes(liveEventWithoutMembership, "unsigned."+strings.ReplaceAll(fieldName, ".", `\.`))
 	if err != nil {
 		t.Fatalf("failed to delete unsigned.membership field")
 	}
@@ -411,11 +421,11 @@ func TestDeleteMSC4115Field(t *testing.T) {
 	stateEvent := testutils.NewStateEvent(t, "m.room.name", "", alice, map[string]interface{}{
 		"name": "Room Name",
 	}, testutils.WithUnsigned(map[string]interface{}{
-		"membership": "join",
+		fieldName: "join",
 	}))
 	stateEventWithoutMembership := make(json.RawMessage, len(stateEvent))
 	copy(stateEventWithoutMembership, stateEvent)
-	stateEventWithoutMembership, err = sjson.DeleteBytes(stateEventWithoutMembership, "unsigned.membership")
+	stateEventWithoutMembership, err = sjson.DeleteBytes(stateEventWithoutMembership, "unsigned."+strings.ReplaceAll(fieldName, ".", `\.`))
 	if err != nil {
 		t.Fatalf("failed to delete unsigned.membership field")
 	}