  The first FORS2 spectropolarimetric observation of the longitudinal magnetic
field of HD54879 of the order of -600G with a lower limit of the dipole
strength of ~2kG dates back to 2014. Since then observations showed a gradual
decrease of the absolute value of the mean longitudinal magnetic field. In the
course of the most recent monitoring of HD54879 using FORS2 spectropolarimetric
observations from 2017 October to 2018 February, a longitudinal magnetic field
strength change from about -300G down to about -90G was reported. A sudden
increase of the absolute value of the mean longitudinal magnetic field and an
accompanying spectral variability was detected on 2018 February 17. New FORS2
spectropolarimetric data obtained from 2018 December to 2019 February confirm
the very slow magnetic field variability, with the field decreasing from about
150G to -100G over two months. Such a slow magnetic field variability, related
to the extremely slow rotation of HD54879, is also confirmed using
high-resolution HARPSpol and ESPaDOnS spectropolarimetry. The re-analysis of
the FORS2 polarimetric spectra from 2018 February indicates that the previously
reported field increase and the change of the spectral appearance was caused by
improper spectra extraction and wavelength calibration using observations
obtained at an insufficient signal-to-noise ratio. The presented properties of
HD54879 are discussed in the context of the Of?p spectral classification.
