The available linguistic studies and normative grammars of Permian and Mari languages define the type of non-finite verb forms classifiable as the gerundive using definitions borrowed from the works of Russian linguists written in the 1950s and 1960s. In general lines those definitions match the Russian language, being based on a ready-made scheme rather than the authentic language material. The result is an extremely simplified description of the Permian and Mari gerundives. Upon a critical analysis of the situation the following extended definition of the word class is given: 1) gerundives are inflected words sharing some properties with verbs, nouns and adverbs; 2) a gerundive may modify either the predicate or the whole clause; 3) a gerundive may either share the subject with the predicate or have its own subject; 4) from the syntactic point of view gerundives function as adverbial modifiers.