Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for storing, in an index associated with a document, a particular term that occurs in the document, wherein the particular term comprises n words, and wherein n is greater than 1; identifying a substitute term of the particular term; and in response to identifying the substitute term of the particular term, storing, in the index associated with the document, (i) the substitute term of the particular term, and (ii) data indicating that the substitute term spans the n words of the particular term.