diff --git a/internal/eventutil/events.go b/internal/eventutil/events.go
index 0f73db2d5..56ee576a0 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 d468dfc98..90f9ff67d 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 8798b62ec..243b2592a 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 1827218b6..746a324fa 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
 	}