Top: redshift distribution of the ERO sample. The black dashed histogram corresponds to the total sample of EROs from Miyazaki et al. (2003), the grey filled histogram indicates the redshift of EROs in the colour–colour window of z ∼ 5.7 LBGs and the red filled histogram shows the sub-sample fainter than z′ = 24.0. The more likely source of contaminants seems to be in the redshift range 1.2 < z < 1.8. Bottom: (R_c − z′) – z′ colour–magnitude diagrams and z′-band magnitude distribution of EROs. Contaminants of the colour selection window are plotted with red solid triangles in the colour–magnitude diagram and red filled histogram in the magnitude distribution plot. All contaminants are the reddest objects of the sample and only 4 of the 11 contaminant objects from the ERO sample are as faint as z > 5 LBGs.