Macro + static: type mismatch in type declaration but not in var declaration

[mratsim]

I'm trying to get some fixed multi-precision integer working.

While trying to create aliases, it seems like macro do not like static arguments in a type declaration context. It works fine however in a variable declaration context:

import macros, typetraits

macro getBase*(bits: static[int]): untyped =
  if bits == 128:
    result = newTree(nnkBracketExpr, ident("MpUintBase"), ident("uint64"))
  else:
    result = newTree(nnkBracketExpr, ident("MpUintBase"), ident("uint32"))

type
  BaseUint* = SomeUnsignedInt or MpUintBase

  MpUintBase*[BaseUint] = object
      lo*, hi*: BaseUint

  ## This gets type mismatch
  MpUint*[bits: static[int]] = getBase(bits)

## This works fine
var foo: getBase(64)
echo foo.type.name