Stable and bioavailable oral dosage forms of ibrutinib, the dosage forms comprising ibrutinib and an acidifying agent. The dosage forms can further comprise a binder, such as sodium alginate, a surfactant, a lubricant, a filler and/or a disintegrant. Methods of treating cancers, particularly blood cancers, and graft versus host disease comprising administering to a patient in need thereof a dosage form comprising ibrutinib and an acidifying agent.