Instantiate C struct on heap

[TencoDK via Digitalmars-d-learn]

Hey,

I'm using DerelictSFML2 + CSFML, I have stuck on instantiating 
window.

derelict/window.d (binding from C):
struct sfWindow;

my_file.d:
sfWindow* sfmlWindow = null;
sfmlWindow = new sfWindow; // ???

This code snippet gives me:
Error: struct derelict.sfml2.window.sfWindow unknown size

How must I create stuctures from C bindings?