Observations of magnetically sensitive lines in the visible and the infrared yield apparently contradictory values for the intrinsic field strength in the internetwork quiet Sun. It is shown that this discrepancy can be understood if one assumes that the magnetic field is not homogeneous over the resolution element. The difference between visible and infrared measurements may be used to set constrains on the subpixel distribution of field strengths. We suggest a specific probability density function that seems to satisfy the existing observational constraints.