The specific heat of Tl₂Ba₂CuO₆ (“2201”) superconducting ceramics with Tc ≈ 90 K is measured in magnetic fields of 0, 0.1, 1, 3, 5, and 14 T. The very small anomaly at the superconducting transition can be described in B = 0 by 2D fluctuations alone, without any measurable mean-field component. Its amplitude is found to decrease rapidly for small fields, and very slowly at large fields while its shape remains symmetrical. The temperature of the top of the anomaly () is field independent. These properties show that the dimensional nature of the phase transition in Tl₂Ba₂CuO₆ is more closely related to that of Bi₂Sr₂CaCu₂O₈ than to that of YBa₂Cu₃O₇. The behavior of the specific-heat anomaly with the field is thermodynamically consistent with previous magnetization measurements.