Despite eighty years of debate, there has been little consensus on 'Greater India's' shape and size prior to its collision with Asia. Indeed the last decade has seen models with S-N extensions ranging between 100 and 2800 km. We argue that the southeast Indian Ocean, where the continent lay when it formed part of Gondwana, is fundamental for constraining Greater India proposals. Using the Wallaby-Zenith Fracture Zone as a guide, we show that extensions north of cratonic India ranged from ∼950 km in the centre to ∼500 and ∼600 km respectively, at the Eastern and Western Syntaxes. The proposal is in agreement with recent seismic modelling of Indian continental lithosphere beneath Tibet.