Mysqli bind_param error

我对我准备好的语句有问题，我已经在堆栈中搜索了答案并尝试了许多无济于事，我已经检查了正确的插入语句，我也尝试将该语句用作似乎有效的常规语句，我得到的错误如下

Fatal error:call to function bind_param()on a non object in ** on line 23

当我对第一个查询使用普通查询时，第二个查询不显示错误

代码是

public function reg_user($name,$username,$password,$email){
        $password = password_hash($password);
        $stmt = $this->db->prepare("SELECT uid FROM users WHERE uname= ? OR uemail = ?");
        $stmt->bind_param("ss", $username,$email);
        $stmt->execute();
        $count_row = $stmt->num_rows; 
        if($count_row == 0){
            $stmt = $this->db->prepare("INSERT INTO users (uname,upass,fullname,uemail) VALUES(?,?,?,?)");
            $stmt->bind_param("ssss", $username,$password,$name,$email); //line 23 
            $return = $stmt->execute();
            return $return;
        } else{
            return false;
        }
    }