We report the detection of sub millimetre radiation from the planetary nebula NGC 7027. The measured flux at 370 μm is in excess of that expected from extrapolating the free–free emission of the H II region and the dust emission seen at 100 μm. This excess is interpreted as arising in a cold (∼ 20 K) dust halo surrounding the planetary nebula. We compare the 370-μm dust optical depth with the gas column densities and optical extinction to NGC 7027. The dust grains responsible for the submillimetre halo emission are similar to those found elsewhere in the interstellar medium, both in the ratio of the visual extinction efficiency to the absorption efficiency at 370 μm and in the abundance relative to the gas. The mass of dust required to produce the 370-μm excess is consistent with the halo mass of ≳ 5M ⊙ deduced by Knapp et al. (1982). This supports their conclusion that the masses of some stars which evolve into white dwarfs rather than supernovae are at least ∼6.5M ⊙ . This is consistent with the suggestion of Weidemann & Koester (1983) that white-dwarf progenitors can have masses up to ∼8M ⊙ .