In this study, we analyzed CB4 and its cation, CB4+. Using CCSD(T)/aug-cc-pVQZ//CCSD(T)/aug-cc-pVTZ quantum-chemical calculations, we found that the neutral molecule is in accord with the results of Boldyrev and Wang, having a C-s global minimum with a planar tricoordinate carbon structure, contradicting previous studies. In contrast, CB4+, which was reported by an early mass spectroscopic study, has a planar tetracoordinate carbon (ptC) atom, demonstrating that a modification of the charge can promote the stabilization of a ptC structure.