Proposed resolution:

This wording is relative to N4762.

1. Change [syserr.syserr.overview] p2, class system_error synopsis, as indicated

   namespace std {
     class system_error : public runtime_error {
     public:
       system_error(error_code ec, const string& what_arg);
       system_error(error_code ec, const char* what_arg);
       explicit system_error(error_code ec);
       system_error(int ev, const error_category& ecat, const string& what_arg);
       system_error(int ev, const error_category& ecat, const char* what_arg);
       system_error(int ev, const error_category& ecat);
       const error_code& code() const noexcept;
       const char* what() const noexcept override;
     };
   }
   

2. Change [syserr.syserr.members] as indicated

   explicit system_error(error_code ec);
   

   -5- Effects: […]

   -6- Ensures: […]

[ 2020-04-07 Issue Prioritization ]

Priority to 3 after reflector discussion.

The constructor for std::system_error taking a single argument of type std::error_code is not marked explicit, which allows implicit conversions from error_code to system_error. I think that this is an oversight and not intentional, and that we should make this constructor explicit.