diff --git a/internal/eventutil/events.go b/internal/eventutil/events.go
index 0f73db2d..56ee576a 100644
--- a/internal/eventutil/events.go
+++ b/internal/eventutil/events.go
@@ -22,6 +22,7 @@ import (
 
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/roomserver/types"
+	"github.com/matrix-org/dendrite/syncapi/synctypes"
 	"github.com/matrix-org/gomatrixserverlib/fclient"
 	"github.com/matrix-org/gomatrixserverlib/spec"
 
@@ -169,13 +170,22 @@ func truncateAuthAndPrevEvents(auth, prev []string) (
 
 // RedactEvent redacts the given event and sets the unsigned field appropriately. This should be used by
 // downstream components to the roomserver when an OutputTypeRedactedEvent occurs.
-func RedactEvent(redactionEvent, redactedEvent gomatrixserverlib.PDU) error {
+func RedactEvent(ctx context.Context, redactionEvent, redactedEvent gomatrixserverlib.PDU, querier api.QuerySenderIDAPI) error {
 	// sanity check
 	if redactionEvent.Type() != spec.MRoomRedaction {
 		return fmt.Errorf("RedactEvent: redactionEvent isn't a redaction event, is '%s'", redactionEvent.Type())
 	}
 	redactedEvent.Redact()
-	if err := redactedEvent.SetUnsignedField("redacted_because", redactionEvent); err != nil {
+	validRoomID, err := spec.NewRoomID(redactionEvent.RoomID())
+	if err != nil {
+		return err
+	}
+	senderID, err := querier.QueryUserIDForSender(ctx, *validRoomID, redactionEvent.SenderID())
+	if err != nil {
+		return err
+	}
+	redactedBecause := synctypes.ToClientEvent(redactionEvent, synctypes.FormatSync, *senderID, redactionEvent.StateKey())
+	if err := redactedEvent.SetUnsignedField("redacted_because", redactedBecause); err != nil {
 		return err
 	}
 	// NOTSPEC: sytest relies on this unspecced field existing :(
diff --git a/syncapi/consumers/roomserver.go b/syncapi/consumers/roomserver.go
index d468dfc9..90f9ff67 100644
--- a/syncapi/consumers/roomserver.go
+++ b/syncapi/consumers/roomserver.go
@@ -151,7 +151,7 @@ func (s *OutputRoomEventConsumer) onMessage(ctx context.Context, msgs []*nats.Ms
 func (s *OutputRoomEventConsumer) onRedactEvent(
 	ctx context.Context, msg api.OutputRedactedEvent,
 ) error {
-	err := s.db.RedactEvent(ctx, msg.RedactedEventID, msg.RedactedBecause)
+	err := s.db.RedactEvent(ctx, msg.RedactedEventID, msg.RedactedBecause, s.rsAPI)
 	if err != nil {
 		log.WithError(err).Error("RedactEvent error'd")
 		return err
diff --git a/syncapi/storage/interface.go b/syncapi/storage/interface.go
index 8798b62e..243b2592 100644
--- a/syncapi/storage/interface.go
+++ b/syncapi/storage/interface.go
@@ -174,7 +174,7 @@ type Database interface {
 	// goes wrong.
 	PutFilter(ctx context.Context, localpart string, filter *synctypes.Filter) (string, error)
 	// RedactEvent wipes an event in the database and sets the unsigned.redacted_because key to the redaction event
-	RedactEvent(ctx context.Context, redactedEventID string, redactedBecause *rstypes.HeaderedEvent) error
+	RedactEvent(ctx context.Context, redactedEventID string, redactedBecause *rstypes.HeaderedEvent, querier api.QuerySenderIDAPI) error
 	// StoreReceipt stores new receipt events
 	StoreReceipt(ctx context.Context, roomId, receiptType, userId, eventId string, timestamp spec.Timestamp) (pos types.StreamPosition, err error)
 	UpdateIgnoresForUser(ctx context.Context, userID string, ignores *types.IgnoredUsers) error
diff --git a/syncapi/storage/shared/storage_consumer.go b/syncapi/storage/shared/storage_consumer.go
index 1827218b..746a324f 100644
--- a/syncapi/storage/shared/storage_consumer.go
+++ b/syncapi/storage/shared/storage_consumer.go
@@ -364,7 +364,7 @@ func (d *Database) PutFilter(
 	return filterID, err
 }
 
-func (d *Database) RedactEvent(ctx context.Context, redactedEventID string, redactedBecause *rstypes.HeaderedEvent) error {
+func (d *Database) RedactEvent(ctx context.Context, redactedEventID string, redactedBecause *rstypes.HeaderedEvent, querier api.QuerySenderIDAPI) error {
 	redactedEvents, err := d.Events(ctx, []string{redactedEventID})
 	if err != nil {
 		return err
@@ -375,7 +375,7 @@ func (d *Database) RedactEvent(ctx context.Context, redactedEventID string, reda
 	}
 	eventToRedact := redactedEvents[0].PDU
 	redactionEvent := redactedBecause.PDU
-	if err = eventutil.RedactEvent(redactionEvent, eventToRedact); err != nil {
+	if err = eventutil.RedactEvent(ctx, redactionEvent, eventToRedact, querier); err != nil {
 		return err
 	}
 
diff --git a/syncapi/storage/storage_test.go b/syncapi/storage/storage_test.go
index bc64aa50..f56e44a3 100644
--- a/syncapi/storage/storage_test.go
+++ b/syncapi/storage/storage_test.go
@@ -10,6 +10,7 @@ import (
 	"testing"
 
 	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/roomserver/api"
 	rstypes "github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/dendrite/setup/config"
 	"github.com/matrix-org/dendrite/syncapi/storage"
@@ -19,6 +20,7 @@ import (
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/gomatrixserverlib/spec"
 	"github.com/stretchr/testify/assert"
+	"github.com/tidwall/gjson"
 )
 
 var ctx = context.Background()
@@ -978,3 +980,52 @@ func TestRecentEvents(t *testing.T) {
 		}
 	})
 }
+
+type FakeQuerier struct {
+	api.QuerySenderIDAPI
+}
+
+func (f *FakeQuerier) QueryUserIDForSender(ctx context.Context, roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
+	return spec.NewUserID(string(senderID), true)
+}
+
+func TestRedaction(t *testing.T) {
+	alice := test.NewUser(t)
+	room := test.NewRoom(t, alice)
+
+	redactedEvent := room.CreateAndInsert(t, alice, "m.room.message", map[string]interface{}{"body": "hi"})
+	redactionEvent := room.CreateEvent(t, alice, spec.MRoomRedaction, map[string]string{"redacts": redactedEvent.EventID()})
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		db, close := MustCreateDatabase(t, dbType)
+		t.Cleanup(close)
+		MustWriteEvents(t, db, room.Events())
+
+		err := db.RedactEvent(context.Background(), redactedEvent.EventID(), redactionEvent, &FakeQuerier{})
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		evs, err := db.Events(context.Background(), []string{redactedEvent.EventID()})
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if len(evs) != 1 {
+			t.Fatalf("expected 1 event, got %d", len(evs))
+		}
+
+		// check a few fields which shouldn't be there in unsigned
+		authEvs := gjson.GetBytes(evs[0].Unsigned(), "redacted_because.auth_events")
+		if authEvs.Exists() {
+			t.Error("unexpected auth_events in redacted event")
+		}
+		prevEvs := gjson.GetBytes(evs[0].Unsigned(), "redacted_because.prev_events")
+		if prevEvs.Exists() {
+			t.Error("unexpected auth_events in redacted event")
+		}
+		depth := gjson.GetBytes(evs[0].Unsigned(), "redacted_because.depth")
+		if depth.Exists() {
+			t.Error("unexpected auth_events in redacted event")
+		}
+	})
+}