Because of different designs, different text input devices have different error patterns. If we consider these aspects when designing an error correction mechanism, we can obtain significantly lower error rates. In this paper, we propose and evaluate a spelling algorithm specifically designed for a five-key chording keyboard. It is based on the maximum a posteriori probability (MAP) criterion, taking into account a dictionary model and the probability that one character is typed for another. These probabilities are determined experimentally. For the considered evaluation text, the proposed method reduced the error rate from 10.11% to 2.17%. As comparison, MsWord and iSpell reduced the error rate to 5.15% and 6.69%, respectively.