Suggested resolution:

1. Change in 7.5.5.2 [expr.prim.lambda.closure] paragraph 5 as follows:

   Given a lambda with a lambda-capture, the type of the explicit object parameter, if any, of the lambda's function call operator (possibly instantiated from a function call operator template) shall be either:

   • the closure type
   • a class type publicly and unambiguously derived from the closure type, or
   • a reference to a possibly cv-qualified such type.

2. Add a new bullet after 13.10.3.1 [temp.deduct.general] bullet 11.10:

   • ...
   • Attempting to create a function type in which a parameter has a type of void, or in which the return type is a function type or array type.
   • Attempting to give an invalid type to an explicit object parameter of a lambda-expression (7.5.5.2 [expr.prim.lambda.closure]).

Subclause 7.5.5.2 [expr.prim.lambda.closure] paragraph 5 restricts the type of an explicit object parameter of a lambda to the closure type or classes derived from the closure type. It neglects to consider ambiguous or private derivation scenarios.