We examine the degree of correspondence between musical and linguistic tone sequences in a corpus of 20 Vietnamese popular songs. Our data suggest that text-setting constraints in Vietnamese, as in some other Asian tone languages, are based primarily on the direction of the pitch transition from one syllable/note to the next. Borrowing some musical terminology, we may say that 'similar motion' is favoured, 'oblique motion' is allowed in certain cases, and 'contrary motion' is disfavoured. As with other Asian tone languages, the definition of these three types of motion depends on the categorisation of the linguistic tones; our current best model achieves a rate of 77% similar motion. We hypothesize that avoidance of contrary motion may be as or more important than achieving correspondence between tonal and melodic transitions in Vietnamese popular song.