Period and amplitude variations of the two main pulsation modes of V391 Peg. The variation of p₁ is compatible with a linear increase up to 2009.0, when a change of regime appears.The same change is also visible for the amplitude: up to 2009.0, a₁ shows a fairly regular sinusoidal shape with a period of about 3400 days or 9.3 years. A linear increase of the pulsation period is visible also for p₂ when considering the whole data set, while the irregular variations of a₂ can be at least partially attributed to the beating between f₂ and . More details are given in the text.