In collaboration with Nubank, we analyzed Datomic Pro 1.0.7075 and found that its inter-transaction safety properties appeared stronger than claimed. Datomic Pro appeared to offer Strong Session Serializable isolation, and Strong Serializable for histories restricted to update transactions. However, Datomic defines unusual intra-transaction semantics in which operations are applied logically concurrent with one another, rather than sequentially. While consistent with Datomic’s documentation, this could cause invariants preserved by individual transaction functions to be broken when those same functions are applied within a single transaction.