diff --git a/state/accumulator.go b/state/accumulator.go
index d8005500..8966f1ca 100644
--- a/state/accumulator.go
+++ b/state/accumulator.go
@@ -399,8 +399,8 @@ func (a *Accumulator) Accumulate(txn *sqlx.Tx, userID, roomID string, prevBatch
 
 	var latestNID int64
 	newEvents := make([]Event, 0, len(eventIDToNID))
-	var redactTheseEventIDs []string
-	for _, ev := range dedupedEvents {
+	redactTheseEventIDs := make(map[string]*Event)
+	for i, ev := range dedupedEvents {
 		nid, ok := eventIDToNID[ev.ID]
 		if ok {
 			ev.NID = int64(nid)
@@ -423,7 +423,7 @@ func (a *Accumulator) Accumulate(txn *sqlx.Tx, userID, roomID string, prevBatch
 					redactsEventID = parsedEv.Get("content.redacts").Str
 				}
 				if redactsEventID != "" {
-					redactTheseEventIDs = append(redactTheseEventIDs, redactsEventID)
+					redactTheseEventIDs[redactsEventID] = &dedupedEvents[i]
 				}
 			}
 			newEvents = append(newEvents, ev)
diff --git a/state/event_table.go b/state/event_table.go
index a793c413..035a4333 100644
--- a/state/event_table.go
+++ b/state/event_table.go
@@ -338,7 +338,11 @@ func (t *EventTable) LatestEventNIDInRooms(txn *sqlx.Tx, roomIDs []string, highe
 	return
 }
 
-func (t *EventTable) Redact(txn *sqlx.Tx, roomVer string, eventIDs []string) error {
+func (t *EventTable) Redact(txn *sqlx.Tx, roomVer string, redacteeEventIDToRedactEvent map[string]*Event) error {
+	eventIDs := make([]string, 0, len(redacteeEventIDToRedactEvent))
+	for e := range redacteeEventIDToRedactEvent {
+		eventIDs = append(eventIDs, e)
+	}
 	// verifyAll=false so if we are asked to redact an event we don't have we don't fall over.
 	eventsToRedact, err := t.SelectByIDs(txn, false, eventIDs)
 	if err != nil {
@@ -357,6 +361,13 @@ func (t *EventTable) Redact(txn *sqlx.Tx, roomVer string, eventIDs []string) err
 		if err != nil {
 			return fmt.Errorf("RedactEventJSON[%s]: %w", eventsToRedact[i].ID, err)
 		}
+		// also set unsigned.redacted_because as EX relies on it
+		eventsToRedact[i].JSON, err = sjson.SetBytes(
+			eventsToRedact[i].JSON, "unsigned.redacted_because", json.RawMessage(redacteeEventIDToRedactEvent[eventsToRedact[i].ID].JSON),
+		)
+		if err != nil {
+			return fmt.Errorf("RedactEventJSON[%s]: setting redacted_because %w", eventsToRedact[i].ID, err)
+		}
 		_, err = txn.Exec(`UPDATE syncv3_events SET event=$1 WHERE event_id=$2`, eventsToRedact[i].JSON, eventsToRedact[i].ID)
 		if err != nil {
 			return fmt.Errorf("cannot update event %s: %w", eventsToRedact[i].ID, err)
diff --git a/state/event_table_test.go b/state/event_table_test.go
index 7d6fb2c8..f6f0a7bb 100644
--- a/state/event_table_test.go
+++ b/state/event_table_test.go
@@ -1063,7 +1063,17 @@ func TestEventTableRedact(t *testing.T) {
 				JSON:                  j,
 			},
 		}, false)
-		assertNoError(t, table.Redact(txn, tc.roomVer, []string{eventID}))
+		assertNoError(t, table.Redact(txn, tc.roomVer, map[string]*Event{
+			eventID: &Event{
+				JSON: json.RawMessage(`{
+					"type": "m.room.redaction",
+					"event_id": "$unimportant",
+					"content": {
+						"redacts": "` + eventID + `"
+					}
+				}`),
+			},
+		}))
 		gots, err := table.SelectByIDs(txn, true, []string{eventID})
 		assertNoError(t, err)
 		if len(gots) != 1 {
@@ -1088,5 +1098,32 @@ func TestEventTableRedactMissingOK(t *testing.T) {
 		t.Fatalf("failed to start txn: %s", err)
 	}
 	defer txn.Rollback()
-	assertNoError(t, table.Redact(txn, "2", []string{"$unknown", "$event", "$ids"}))
+	assertNoError(t, table.Redact(txn, "2", map[string]*Event{
+		"$unknown": {
+			JSON: json.RawMessage(`{
+				"type": "m.room.redaction",
+				"event_id": "$unimportant",
+				"content": {
+					"redacts": "$unknown"
+				}
+			}`),
+		},
+		"$event": {
+			JSON: json.RawMessage(`{
+				"type": "m.room.redaction",
+				"event_id": "$unimportant",
+				"content": {
+					"redacts": "$event"
+				}
+			}`),
+		},
+		"$ids": {
+			JSON: json.RawMessage(`{
+				"type": "m.room.redaction",
+				"event_id": "$unimportant",
+				"content": {
+					"redacts": "$ids"
+				}
+			}`),
+		}}))
 }
diff --git a/tests-e2e/main_test.go b/tests-e2e/main_test.go
index 2ea63800..e6b42491 100644
--- a/tests-e2e/main_test.go
+++ b/tests-e2e/main_test.go
@@ -77,6 +77,15 @@ func eventsEqual(wantList []Event, gotList []json.RawMessage) error {
 		if want.Sender != "" && want.Sender != got.Sender {
 			return fmt.Errorf("event %d Sender mismatch: got %v want %v", i, got.Sender, want.Sender)
 		}
+		// loop each key on unsigned as unsigned also includes "age" which is unpredictable so cannot DeepEqual
+		if want.Unsigned != nil {
+			for k, v := range want.Unsigned {
+				got := got.Unsigned[k]
+				if !reflect.DeepEqual(got, v) {
+					return fmt.Errorf("event %d Unsigned.%s mismatch: got %v want %v", i, k, got, v)
+				}
+			}
+		}
 	}
 	return nil
 }
@@ -218,3 +227,10 @@ func registerNamedUser(t *testing.T, localpartPrefix string) *CSAPI {
 func ptr(s string) *string {
 	return &s
 }
+
+func assertEqual(t *testing.T, msg string, got, want interface{}) {
+	t.Helper()
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("%s: got %v want %v", msg, got, want)
+	}
+}
diff --git a/tests-e2e/redaction_test.go b/tests-e2e/redaction_test.go
index 090dbf33..54af73ca 100644
--- a/tests-e2e/redaction_test.go
+++ b/tests-e2e/redaction_test.go
@@ -5,6 +5,7 @@ import (
 
 	"github.com/matrix-org/sliding-sync/sync3"
 	"github.com/matrix-org/sliding-sync/testutils/m"
+	"github.com/tidwall/gjson"
 )
 
 func TestRedactionsAreRedactedWherePossible(t *testing.T) {
@@ -59,5 +60,18 @@ func TestRedactionsAreRedactedWherePossible(t *testing.T) {
 			{ID: redactionEventID},
 		})},
 	}))
+	// introspect the unsigned key a bit more, we don't know all the fields so can't use a matcher
+	gotEvent := gjson.ParseBytes(res.Rooms[room].Timeline[len(res.Rooms[room].Timeline)-2])
+	redactedBecause := gotEvent.Get("unsigned.redacted_because")
+	if !redactedBecause.Exists() {
+		t.Fatalf("unsigned.redacted_because must exist, but it doesn't. Got: %v", gotEvent.Raw)
+	}
+	// assert basic fields
+	assertEqual(t, "event_id mismatch", redactedBecause.Get("event_id").Str, redactionEventID)
+	assertEqual(t, "sender mismatch", redactedBecause.Get("sender").Str, alice.UserID)
+	assertEqual(t, "type mismatch", redactedBecause.Get("type").Str, "m.room.redaction")
+	if !redactedBecause.Get("content").Exists() {
+		t.Fatalf("unsigned.redacted_because.content must exist, but it doesn't. Got: %v", gotEvent.Raw)
+	}
 
 }