The XIAM code is one of the most frequently used programs to treat the microwave spectra of molecules with up to three methyl internal rotors. XIAM is user-friendly and fast, but often shows difficulties in dealing with low torsional barriers. An example is the case of m-methylanisole where the methyl group attached at the meta-position of the ring undergoes internal rotation with a barrier height of about 56 cm−1 for the cis conformer and 37 cm−1 for the trans conformer. The standard deviation obtained with XIAM is much larger than the measurement accuracy for both conformers. Recently, the code has been modified, and three higher order effective parameters connected to the potential term cos(3α) were implemented, which reduced the standard deviations of the fits to almost measurement accuracy.