In this paper, we present a stochastic part-of-speech tagger for Turkish. The tagger is primarily developed for information retrieval purposes, but it can as well serve as a light-weight PoS tagger for other purposes. The tagger uses a well-established Hidden Markov model of the language with a closed lexicon that consists of fixed number of letters from the word endings. We have considered seven different lengths of word endings against 30 training corpus sizes. Best-case accuracy obtained is 90.2% with 5 characters. The main contribution of this paper is to present a way of constructing a closed vocabulary for part-of-speech tagging effort that can be useful for highly inflected languages like Turkish, Finnish, Hungarian, Estonian, and Czech.