Complete and incomplete fusion cross sections for ⁶Li + ¹⁵⁹Tb have been measured at energies around the Coulomb barrier by the γ -ray method. The measurements show that the complete fusion cross sections at above-barrier energies are suppressed by ∼34% compared to coupled-channel calculations. A comparison of the complete fusion cross sections at above-barrier energies with the existing data for ^11,10B + ¹⁵⁹Tb and ⁷Li + ¹⁵⁹Tb shows that the extent of suppression is correlated with the α separation energies of the projectiles. It has been argued that the Dy isotopes produced in the reaction ⁶Li + ¹⁵⁹Tb at below-barrier energies are primarily due to the d transfer to unbound states of ¹⁵⁹Tb, while both transfer and incomplete fusion processes contribute at above-barrier energies.