I defend Spinoza's claim that extension is an attribute that an indivisible substance, such as God, could have. However, in order to explain why, we must abandon two long held orthodoxies in Spinoza scholarship. First, Spinoza acknowledges only parts that do not depend on their whole. Second, God, considered as natura naturans, has no parts of any kind. Against these orthodoxies, I show that having parts which depend on their whole, for Spinoza, does not entail divisibility and that God, considered (...) as natura naturans, must have such parts in order to be extended. Along the way, we will have a closer look at Spinoza’s mereology and address apparently conflicting statements that Spinoza makes about the relation of part and whole that have long vexed commentators. (shrink)