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The motion of a disk in a Langmuir film bounding a liquid substrate is a classical hydrodynamic problem, dating back to Saffman (J. Fluid Mech., vol. 73, 1976, p. 593) who focused upon the singular problem of translation at large Boussinesq number,$${\textit {Bq}}\gg 1$$. A semianalytic solution of the dual integral equations governing the flow at arbitrary$${\textit {Bq}}$$was devised by Hugheset al.(J. Fluid Mech., vol. 110, 1981, p. 349). When degenerated to the inviscid-film limit$${\textit {Bq}}\to 0$$, it produces the value$$8$$for the dimensionless translational drag, which is$$50\,\%$$larger than the classical$$16/3$$-value corresponding to a free surface. While that enhancement has been attributed to surface incompressibility, the mathematical reasoning underlying the anomaly has never been fully elucidated. Here we address the inviscid limit$${\textit {Bq}}\to 0$$from the outset, revealing a singular mechanism where half of the drag is contributed by the surface pressure. We proceed beyond that limit, considering a nearly inviscid film. A naïve attempt to calculate the drag correction using the reciprocal theorem fails due to an edge singularity of the leading-order flow. We identify the formation of a boundary layer about the edge of the disk, where the flow is primarily in the azimuthal direction with surface and substrate stresses being asymptotically comparable. Utilising the reciprocal theorem in a fluid domain tailored to the asymptotic topology of the problem produces the drag correction$$(8\,{\textit {Bq}}/{\rm \pi} ) [ \ln (2/{\textit {Bq}}) + \gamma _E+1]$$,$$\gamma _E$$being the Euler–Mascheroni constant.