we study the relation between the petersson norm of a holomorphic gl(2) form $f$ and that of its (suitably normalized) jacquet-langlands lift $g$ to a shimura curve. the ratio of these two norms was previously shown to be algebraic by shimura and rational by harris-kudla. we prove an integrality result for this ratio and explain the arithmetic significance of this ratio in terms of certain congruences satisfied by $f$