  In the gravitational lens system Q2237+0305 the cruciform quasar image
geometry is twisted by ten degrees by the lens effect of a bar in the lensing
galaxy. This effect can be used to measure the mass of the bar. We construct a
new lensing model for this system with a power-law elliptical bulge and a
Ferrers bar. The observed ellipticity of the optical isophotes of the galaxy
leads to a nearly isothermal elliptical profile for the bulge with a total
quasar magnification of 16^{+5}_{-4}. We measure a bar mass of 7.5\pm1.5 \times
10^8 h^{-1}_{75} M_{\sun} in the region inside the quasar images.
