https://issues.dlang.org/show_bug.cgi?id=12744
--- Comment #1 from Tomer Filiba <tomerfil...@gmail.com> --- happens on dmd 2.66.1 as well: void f(int x, out int y) { } void g(ref ParameterTypeTuple!f params) { f(params); } dmd: mtype.c:9529: void Parameter::toDecoBuffer(OutBuffer*): Assertion `0' failed. [1] 14388 abort (core dumped) dmd source/main.d --