Like other Germanic languages, Frisian has both strong and weak verbal inflection. Despite a strong diachronic tendency for change towards weak inflection, strong inflection patterns are available synchronically to speakers to form the past tense and past participle of new or nonce verbs. Using a measure for ‘potential productivity’ developed by Knooihuizen and Strik (Folia Linguist Hist 35:173–200, 2014) for Dutch, we investigate the relative strength of available patterns in Frisian in an elicitation and an acceptability judgment experiment. Despite the multitude of different patterns in the strong verbal inflection system, strong inflection makes up 35% of the elicited nonce forms; these forms cannot all be explained by analogy. Analogically formed strong inflections of nonce verbs receive relatively high acceptability ratings at 4.2 on a 7-point scale. The elicitation experiment also produced many weak forms (12% of participles) that are not normatively possible with the -e infinitives in the elicitation prompt. These alternative weak forms were not included in the acceptability judgment experiment. We discuss the experimental results in the context of diachronically attested language change in Frisian and of intensive language contact with Dutch.