The invention is directed to novel anhydrous crystalline butenedioate salt form 1 of Compound I, which is a modulator of muscarinic M1 receptors. The novel crystalline forms of compound I are useful in the treatment or prevention of Alzheimers disease and other disorders and diseases in which muscarinic M1 receptors are involved. The invention is further directed to pharmaceutical compositions comprising the novel crystalline forms of Compound I.