  We compute Yukawa couplings in type IIa string theory compactified on a
six-torus in the presence of intersecting D6-branes. The six-torus is generated
by an SO(12) root lattice. Yukawa couplings are expressed as sums over
worldsheet instantons. Our result extends known expressions to a
non-factorisable torus. As an aside we also fill in some details for the
factorisable torus and non-coprime intersection numbers.
