In Middle English (ME), manner of motion verbs occur in perfect periphrases with both BE and HAVE as auxiliaries (e.g. is/has run, is/has ridden), the BE-variant being the older, the HAVE-variant the more recent form with these verbs. Los (2015) hypothesizes that the choice of auxiliary with manner of motion verbs in ME might depend systematically on aktionsart in that HAVE is chosen when the verb denotes a controlled process (e.g. he has run fast for an hour), and BE when the verb denotes a change of location (e.g. he is run into town), much as in Present-Day Dutch. Also taking into account other factors that have been suggested to influence the choice of BE vs. HAVE in Middle English (such as counterfactuality, infinitive, or past perfect), I test this hypothesis on data from the Corpus of Middle English Prose and Verse. I show that aktionsart is indeed a very reliable predictor, but overridden by counterfactuality.