Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for correcting potentially inaccurate terms in queries. In an aspect, a search system determines that an original query includes a potentially inaccurate term. The determination is made on the basis that the term of the original query meets an inaccuracy criterion. Derivative queries are generated from the original query. Each derivative query does not include the potentially inaccurate term. For each derivative query resources that are determined to be responsive to the derivative query are determined, and from the resources, a corrected term is determined. The corrected term is substituted for the potentially inaccurate term, and a search operation that uses the corrected query as input is performed.