Context : The extrasolar planet WASP-67 b is the first hot Jupiter definitively known to undergo only partial eclipses .
The lack of the second and third contact point in this planetary system makes it difficult to obtain accurate measurements of its physical parameters .

Aims : By using new high-precision photometric data , we confirm that WASP-67 b shows grazing eclipses and compute accurate estimates of the physical properties of the planet and its parent star .

Methods : We present high-quality , multi-colour , broad-band photometric observations comprising five light curves covering two transit events , obtained using two medium-class telescopes and the telescope-defocussing technique .
One transit was observed through a Bessel- R filter and the other simultaneously through filters similar to Sloan g ^ { \prime } r ^ { \prime } i ^ { \prime } z ^ { \prime } .
We modelled these data using jktebop .
The physical parameters of the system were obtained from the analysis of these light curves and from published spectroscopic measurements .

Results : All five of our light curves satisfy the criterion for being grazing eclipses .
We revise the physical parameters of the whole WASP-67 system and , in particular , significantly improve the measurements of the planet ’ s radius ( R _ { \mathrm { b } } = 1.091 \pm 0.046 R _ { \mathrm { Jup } } ) and density ( \rho _ { \mathrm { b } } = 0.292 \pm 0.036 \rho _ { \mathrm { Jup } } ) , as compared to the values in the discovery paper ( R _ { \mathrm { b } } = 1.4 _ { -0.2 } ^ { +0.3 } R _ { \mathrm { Jup } } and \rho _ { \mathrm { b } } = 0.16 \pm 0.08 \rho _ { \mathrm { Jup } } ) .
The transit ephemeris was also substantially refined .
We investigated the variation of the planet ’ s radius as a function of the wavelength , using the simultaneous multi-band data , finding that our measurements are consistent with a flat spectrum to within the experimental uncertainties .

Conclusions :