The invention relates to hardenable ceramic bone substitute compositions having improved setting, powders for such compositions and methods for their manufacture and use in medical treatment. More specifically the invention relates to hardenable bone substitute powder and hardenable bone substitute paste with improved setting properties, comprising calcium sulfate and heat-treated hydroxyapatite (passivated HA), which bone substitute is suitable for treatment of disorders of supportive tissue such as bone loss, bone fracture, bone trauma and osteomyelitis.