No it doesn't fit.
It does however have enough plastic loops attached that you can easily use a couple of Toe-Straps to hang it off the rails.
You can push the straps under the bracket (that the saddle-rail adapter is supposed to slide into) so it hangs from the same point. Then I use another one, from a plastic loop at the rear of the bag, to loop around rails and provide a bit more support.
Using toe-straps also gives you a handy option of clipping the 2 buckles together, behind one of the straps, to prevent the roll-top closure unwinding.
In the world of efficient Ortlieb bags, the Brooks saddle, Toe-strap, solution to this saddlebag is not very elegant. But it works OK.
