  Within the framework of a low-energy effective field theory we consider the
procedure of extraction of the S-wave kaon-nucleon scattering lengths a0 and a1
from a combined fit to the kaonic hydrogen and kaonic deuterium data. It is
demonstrated that, if the present DEAR central values for the kaonic hydrogen
ground-state energy and width are used in the analysis of the data, a solution
for a0 and a1 exists only in a restricted domain of input values for the
kaon-deuteron scattering length. We therefore conclude that forthcoming
measurement of this scattering length imposes stringent constraints on the
theoretical description of the kaon-deuteron interactions at low energies.
