A solution (600b) for auto-completing words being input to a computer is proposed. For this purpose, a user starts inputting (656;677) a prefix of a target word; the computer tries predicting the target word that is desired, and it completes (680) the prefix automatically (without the need of inputting the entire target word). In the proposed solution, the user also inputs (659-662,665) an indication of the length of the target word. In this way, the computer can restrict (668) the words being eligible to complete the prefix (i.e., including it) only to the ones having the desired length. This allows solving any ambiguity with shorter prefixes.