Sample program:

import std.typecons;

typedef uint oid_t;

void main() {
    // Tuple!(uint,uint) key; // Works
    Tuple!(oid_t,oid_t) key; // Doesn't work
}

Error observed when compiling when using DMD 2.052:

/path/to/src/phobos/std/format.d(1579): Error: function std.format.formatValue!(Appender!(string),oid_t,immutable(char)).formatValue is deprecated
/path/to/src/phobos/std/format.d(306): Error: template instance std.format.formatGeneric!(Appender!(string),oid_t,immutable(char)) error instantiating
/path/to/src/phobos/std/typecons.d(507):        instantiated from here: formattedWrite!(Appender!(string),immutable(char),oid_t)