InSituRegion + allocatorObject compile time error

[ref2401 via Digitalmars-d-learn]

Getting this error, could someone explain why?

void main(string[] args) {
	InSituRegion!(1024) stackAlloc;
	IAllocator alloc = allocatorObject(stackAlloc);
}

..\src\phobos\std\conv.d(5055):
Error: static assert  "Don't know how to initialize an object of 
type CAllocatorImpl!(InSituRegion!(1024u, 8u), cast(Flag)false) 
with arguments (InSituRegion!(1024u, 8u))"

..\src\phobos\std\experimental\allocator\package.d(1175):
instantiated from here: 
emplace!(CAllocatorImpl!(InSituRegion!(1024u, 8u), 
cast(Flag)false), InSituRegion!(1024u, 8u))

main.d(15):
instantiated from here: allocatorObject!(InSituRegion!(1024u, 8u))

Thank you