Pdb2gmx does not recognize GBUT

GROMACS version:2022
GROMACS modification: Yes/No

I have a peptide with GBUT (2-amino-4-guanidinobutryric acid) residue which is in the charmm36 ff. I have put the GBUT in the residuetypes.dat, but pdb2gmx still thinks that I have a GBU residue.
Any suggestions?
Sandor