diff --git a/roomserver/auth/auth.go b/roomserver/auth/auth.go
index b6168d38b..ba10a4332 100644
--- a/roomserver/auth/auth.go
+++ b/roomserver/auth/auth.go
@@ -13,6 +13,9 @@
 package auth
 
 import (
+	"context"
+
+	"github.com/matrix-org/dendrite/roomserver/storage"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/gomatrixserverlib/spec"
 )
@@ -22,6 +25,7 @@ import (
 // IsServerAllowed returns true if the server is allowed to see events in the room
 // at this particular state. This function implements https://matrix.org/docs/spec/client_server/r0.6.0#id87
 func IsServerAllowed(
+	ctx context.Context, db storage.RoomDatabase,
 	serverName spec.ServerName,
 	serverCurrentlyInRoom bool,
 	authEvents []gomatrixserverlib.PDU,
@@ -37,7 +41,7 @@ func IsServerAllowed(
 		return true
 	}
 	// 2. If the user's membership was join, allow.
-	joinedUserExists := IsAnyUserOnServerWithMembership(serverName, authEvents, spec.Join)
+	joinedUserExists := IsAnyUserOnServerWithMembership(ctx, db, serverName, authEvents, spec.Join)
 	if joinedUserExists {
 		return true
 	}
@@ -46,7 +50,7 @@ func IsServerAllowed(
 		return true
 	}
 	// 4. If the user's membership was invite, and the history_visibility was set to invited, allow.
-	invitedUserExists := IsAnyUserOnServerWithMembership(serverName, authEvents, spec.Invite)
+	invitedUserExists := IsAnyUserOnServerWithMembership(ctx, db, serverName, authEvents, spec.Invite)
 	if invitedUserExists && historyVisibility == gomatrixserverlib.HistoryVisibilityInvited {
 		return true
 	}
@@ -70,7 +74,7 @@ func HistoryVisibilityForRoom(authEvents []gomatrixserverlib.PDU) gomatrixserver
 	return visibility
 }
 
-func IsAnyUserOnServerWithMembership(serverName spec.ServerName, authEvents []gomatrixserverlib.PDU, wantMembership string) bool {
+func IsAnyUserOnServerWithMembership(ctx context.Context, db storage.RoomDatabase, serverName spec.ServerName, authEvents []gomatrixserverlib.PDU, wantMembership string) bool {
 	for _, ev := range authEvents {
 		if ev.Type() != spec.MRoomMember {
 			continue
@@ -85,12 +89,12 @@ func IsAnyUserOnServerWithMembership(serverName spec.ServerName, authEvents []go
 			continue
 		}
 
-		_, domain, err := gomatrixserverlib.SplitID('@', *stateKey)
+		userID, err := db.GetUserIDForSender(ctx, ev.RoomID(), spec.SenderID(*stateKey))
 		if err != nil {
 			continue
 		}
 
-		if domain == serverName {
+		if userID.Domain() == serverName {
 			return true
 		}
 	}
diff --git a/roomserver/auth/auth_test.go b/roomserver/auth/auth_test.go
index e3eea5d8b..192d9e5da 100644
--- a/roomserver/auth/auth_test.go
+++ b/roomserver/auth/auth_test.go
@@ -1,13 +1,23 @@
 package auth
 
 import (
+	"context"
 	"testing"
 
+	"github.com/matrix-org/dendrite/roomserver/storage"
 	"github.com/matrix-org/dendrite/test"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/gomatrixserverlib/spec"
 )
 
+type FakeStorageDB struct {
+	storage.RoomDatabase
+}
+
+func (f *FakeStorageDB) GetUserIDForSender(ctx context.Context, roomID string, senderID spec.SenderID) (*spec.UserID, error) {
+	return spec.NewUserID(string(senderID), true)
+}
+
 func TestIsServerAllowed(t *testing.T) {
 	alice := test.NewUser(t)
 
@@ -77,7 +87,7 @@ func TestIsServerAllowed(t *testing.T) {
 				authEvents = append(authEvents, ev.PDU)
 			}
 
-			if got := IsServerAllowed(tt.serverName, tt.serverCurrentlyInRoom, authEvents); got != tt.want {
+			if got := IsServerAllowed(context.Background(), &FakeStorageDB{}, tt.serverName, tt.serverCurrentlyInRoom, authEvents); got != tt.want {
 				t.Errorf("IsServerAllowed() = %v, want %v", got, tt.want)
 			}
 		})
diff --git a/roomserver/internal/helpers/helpers.go b/roomserver/internal/helpers/helpers.go
index eee8e1a55..d263353e3 100644
--- a/roomserver/internal/helpers/helpers.go
+++ b/roomserver/internal/helpers/helpers.go
@@ -95,7 +95,7 @@ func IsServerCurrentlyInRoom(ctx context.Context, db storage.Database, serverNam
 	for i := range events {
 		gmslEvents[i] = events[i].PDU
 	}
-	return auth.IsAnyUserOnServerWithMembership(serverName, gmslEvents, spec.Join), nil
+	return auth.IsAnyUserOnServerWithMembership(ctx, db, serverName, gmslEvents, spec.Join), nil
 }
 
 func IsInvitePending(
@@ -289,7 +289,7 @@ func CheckServerAllowedToSeeEvent(
 			return false, err
 		}
 	}
-	return auth.IsServerAllowed(serverName, isServerInRoom, stateAtEvent), nil
+	return auth.IsServerAllowed(ctx, db, serverName, isServerInRoom, stateAtEvent), nil
 }
 
 func slowGetHistoryVisibilityState(
diff --git a/roomserver/internal/perform/perform_backfill.go b/roomserver/internal/perform/perform_backfill.go
index 388150936..8e87359a3 100644
--- a/roomserver/internal/perform/perform_backfill.go
+++ b/roomserver/internal/perform/perform_backfill.go
@@ -582,7 +582,7 @@ func joinEventsFromHistoryVisibility(
 	}
 
 	// Can we see events in the room?
-	canSeeEvents := auth.IsServerAllowed(thisServer, true, events)
+	canSeeEvents := auth.IsServerAllowed(ctx, db, thisServer, true, events)
 	visibility := auth.HistoryVisibilityForRoom(events)
 	if !canSeeEvents {
 		logrus.Infof("ServersAtEvent history not visible to us: %s", visibility)