Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Machine (EVM). In versions 0.2.15, 0.2.16 and 0.3.0, named re-entrancy locks are allocated incorrectly. Each function using a named re-entrancy lock gets a unique lock regardless of the key, allowing cross-function re-entrancy in contracts compiled with the susceptible versions. A specific set of conditions is required to result in misbehavior of affected contracts, specifically: a ".vy" contract compiled with "vyper" versions "0.2.15", "0.2.16", or "0.3.0"; a primary function that utilizes the "@nonreentrant" decorator with a specific "key" and does not strictly follow the check-effects-interaction pattern (i.e. contains an external call to an untrusted party before storage updates); and a secondary function that utilizes the same "key" and would be affected by the improper state caused by the primary function. Version 0.3.1 contains a fix for this issue.