According to 14.5 [except.spec] paragraph 14,

An implicitly declared special member function (11.4.4 [special]) shall have an exception-specification. If f is an implicitly declared default constructor, copy constructor, move constructor, destructor, copy assignment operator, or move assignment operator, its implicit exception-specification specifies the type-id T if and only if T is allowed by the exception-specification of a function directly invoked by f's implicit definition; f shall allow all exceptions if any function it directly invokes allows all exceptions, and f shall allow no exceptions if every function it directly invokes allows no exceptions.

It would be clearer if this description made explicit the intent that special member functions that invoke no other functions are to allow no exceptions.