This paper evaluates recent developments in the inflection of Frisian past participles and how to account for them with the aid of a model of morphological productivity. In Frisian, there are two alternative types of past participles which both have their origin in the South-western dialect region of Fryslân, but of which only one is spreading productively across the whole language area. The natural existence of contact between the original dialect region and the rest of the language area, in theory enables both alternative types to spread. Also, both of them can be described with rules. We will therefore argue that the reason for the spread of only one of the alternatives is due to the productivity of its underlying rule. Specifically, we will argue that the Tolerance Principle (Yang, Linguis Var Yearb 5(1):265–302, 2005, The price of linguistic productivity: how children learn to break the rules of language. MIT Press, 2016) predicts both the difference in productivity between the two alternatives, as well as the productive spread of one of the alternatives outwards from the dialect region in which it originated