diff --git a/sam/repository/message.go b/sam/repository/message.go
index 5afb60dc5..bcc6cab42 100644
--- a/sam/repository/message.go
+++ b/sam/repository/message.go
@@ -199,6 +199,10 @@ func (r *message) PrefillThreadParticipants(mm types.MessageSet) error {
 		UserID  uint64 `db:"rel_user"`
 	}{}
 
+	if len(mm) == 0 {
+		return nil
+	}
+
 	if sql, args, err := sqlx.In(sqlThreadParticipantsByMessageID, mm.IDs()); err != nil {
 		return err
 	} else if err = r.db().Select(&rval, sql, args...); err != nil {
diff --git a/sam/repository/message_flag.go b/sam/repository/message_flag.go
index 1e18e8b41..70e648628 100644
--- a/sam/repository/message_flag.go
+++ b/sam/repository/message_flag.go
@@ -63,6 +63,10 @@ func (r *messageFlag) FindByFlag(messageID, userID uint64, flag string) (*types.
 func (r *messageFlag) FindByMessageIDs(IDs ...uint64) ([]*types.MessageFlag, error) {
 	rval := make([]*types.MessageFlag, 0)
 
+	if len(IDs) == 0 {
+		return rval, nil
+	}
+
 	sql := `SELECT * FROM message_flags WHERE rel_message IN (?)`
 
 	if sql, args, err := sqlx.In(sql, IDs); err != nil {