This article presents a simple yet efficient method for solving lemma ambiguity as a part of morphological tagging of Estonian. By lemma ambiguity authors mean the situation when a word-form has several (mostly two) possible morphological readings and the only difference between these readings lies in the correct form of lemma, i.e. the POS and grammatical categories are the same, but possible lemmas are different. This type of ambiguity is characteristic of 1.5% of tokens in an otherwise morphologically disambiguated text. A text- and corpus-based method is used to disambiguate this kind of ambiguity. The precision of the method is 0.94 and recall 0.67.