Using a fibre bundle approach as in the work of Wu and Yang (1975) one finds that the charge quantisation condition for two dyons each with Dirac magnetic charge g_i and charge q_i is q₁g₂=1/2cn₁ and q₂g₁=1/2cn₂, where n₁ and n₂ are integers. This is more restrictive than the condition q₁g₂-q₂g₁=cn found by Schwinger (1966) and Zwanziger (1968) using an infinite string of singularities. The condition does not allow a new elementary unit of electric charge for dyons contrary to their condition. The quantisation condition agrees with the result one would obtain using a minimal, semi-infinite string of singularities, just as the result of Wu and Yang agrees with the Dirac version of the quantisation condition but not the Schwinger version for the case of an uncharged magnetic monopole.