Relation between metallicity and stellar-to-gas mass ratio. Metallicity is given in the calibration of KK04. The dashed line is the relation found by Zahid et al. (2014) for star-forming galaxies. Gas (hydrogen) masses are computed using Eq. (34) in Zahid et al. (2014). Errors on the x-axis only take into account the errors on measured M_⋆: the true errors are larger due to the error in metallicity calibration (~0.15 dex) and the scatter in the relation itself (~0.07 dex). Blue data show the BAT6 sample, red represent the Levesque et al. (2010a) sample, and grey dots the values computed from the VVDS sample (only log M_⋆> 9.5, which allows the assumption that all correct KK04 values are of the upper branch). It is evident that the biased sample used by Levesque et al. (2010a) lies below the median relation of star-forming galaxies. While a few of our own LGRB hosts seem to be outliers, most of our hosts are consistent within errors with the relation.