This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
According to 15.6 [cpp.replace] paragraph 4,
If the identifier-list in the macro definition does not end with an ellipsis, the number of arguments (including those arguments consisting of no preprocessing tokens) in an invocation of a function-like macro shall equal the number of parameters in the macro definition.
That is, a sequence of no preprocessing tokens counts as an argument. That phrasing has problems with zero-argument function-like macros, e.g.,
#define M() M();
M is defined as having no parameters but the invocation has one (empty) argument, which does not match the number of parameters in the definition.