The rotational spectrum of the heterodimer oxetane HF has been investigated by means of molecular beam Fourier-transform microwave spectroscopy (MB-FTMW) in the frequency range 6-26 GHz. The spectra of (C3H6O)-C-12 . . . HF, alpha -(13) (CC2H6O)-C-12 . . . HF and beta-(CC2H6O)-C-13-C-12 . . . HF have been analysed. The results provide evidence that the measurements reported in the previous microwave investigation [A.S. Georgiou et al., J. Mel. Struct. 69 (1980) 69] do not belong to this complex. A C-s symmetry has been established with HF lying in the symmetry plane bisecting the COC ring angle. A planar ring configuration of oxetane subunit in the complex has been determined showing no significant structural changes upon complexation.