Buy smaller - the straps are too generous and with not enough adjustment.  I normally wear a size 9 shoe, which translates to a 39 (8.5 to small 9). I tried on both a 38 and 39 in the shoe store and could not keep the 39 on my feet.  I also could not tighten the one adjustable strap enough to keep the shoe on my foot so I ended up with the 38, which is fine for a sandal that is open toed.  Bought the black which is dressy and quite nice for an MBT!