Context : Stellar rotation affects the transport of chemical elements and angular momentum and is therefore a key process during stellar evolution , which is still not fully understood . This is especially true for massive OB-type stars , which are important for the chemical enrichment of the universe . It is therefore important to constrain the physical parameters and internal angular momentum distribution of massive OB-type stars to calibrate stellar structure and evolution models . Stellar internal rotation can be probed through asteroseismic studies of rotationally split non radial oscillations but such results are still quite rare , especially for stars more massive than the Sun . The slowly pulsating B9V star HD 201433 is known to be part of a single-lined spectroscopic triple system , with two low-mass companions orbiting with periods of about 3.3 and 154 days . Aims : Our goal is to measure the internal rotation profile of HD 201433 and investigate the tidal interaction with the close companion . Methods : We used probabilistic methods to analyse the BRITE - Constellation photometry and radial velocity measurements , to identify a representative stellar model , and to determine the internal rotation profile of the star . Results : Our results are based on photometric observations made by BRITE - Constellation and the Solar Mass Ejection Imager on board the Coriolis satellite , high-resolution spectroscopy , and more than 96 years of radial velocity measurements . We identify a sequence of nine frequency doublets in the photometric time series , consistent with rotationally split dipole modes with a period spacing of about 5030 s. We establish that HD 201433 is in principle a solid-body rotator with a very slow rotation period of 297 \pm 76 days . Tidal interaction with the inner companion has , however , significantly accelerated the spin of the surface layers by a factor of approximately one hundred . The angular momentum transfer onto the surface of HD 201433 is also reflected by the statistically significant decrease of the orbital period of about 0.9 s during the last 96 years . Conclusions : Combining the asteroseismic inferences with the spectroscopic measurements and the orbital analysis of the inner binary system , we conclude that tidal interactions between the central SPB star and its inner companion have almost circularised the orbit . They have , however , not yet aligned all spins of the system and have just begun to synchronise rotation .