This article takes a close look at pseudo-correlatives: multiple sentences in Middle Russian with the pronoun kotoryj ‘which’ in the first clause. It will be argued that they lack correlatives features and that korotyj in such constructions was not a relative but an indefinite pronoun, like the Russian nekotoryj, koe-kakoj. The pseudo-correlatives of Middle Russian are the result of the intermediate stage of the process of the grammaticalization of kotoryj from indefinite to relative pronoun that caused the transformation of the compound constructions into the complex sentence.