The Domainslib library for multicore OCaml provides support for fine-grained parallel programming by implementing lightweight parallel tasks with a work stealing scheduler. This talk motivates an extension to Domainslib which allows tasks to be assigned priorities, with higher-priority tasks scheduled preferentially over lower-priority tasks. The extension, called Priodomainslib, implements a priority-based work stealing scheduler and provides a wrapper around mutexes allowing for safe synchronization without priority inversions. Existing code using Domainslib can use Priodomainslib (at a single priority) with no modifications.