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We have scrupulously investigated the high-pressure structural behaviour of the topological Kondo insulator SmB6 through synchrotron powder x-ray diffraction. Lattice modifications are observed at a critical pressure of for three separate compression experiments at ambient and low temperatures. The initially subtle compression of the Sm-B bond length shows a sharp kink downward at the critical pressure. These anomalies coincide with the phase diagram boundaries for the pressure-induced metallization and the concurrent appearance of long-range magnetic ordering in the compound. We propose a scenario of delocalization of 4f electrons and the gradual filling of 5d conduction bands, which can also provide some clarification on the valence dependence of Sm with pressure. [ABSTRACT FROM AUTHOR]