When constrained by the zero lower bound, some central banks have communicated a threshold that must be met before short-term interest rates would be permitted to rise. Simulation results for Canada show that forward guidance that is conditional on achieving a price-level threshold can theoretically raise demand and inflation expectations by significantly more than unemployment thresholds. This superior performance is attributable to the fact that the price-level threshold depends on past inflation outcomes. In practice, however, history-dependent thresholds such as this might be more challenging for central banks to communicate.