This paper explores the effect of manipulating the internal structure of a complex subject on the incidence of subject--verb agreement errors. Using the sentence completion task (Bock & Miller, 1991), this study followed up on Vigliocco and Nicol's (1995) finding that the syntactic distance between a head noun and a number-mismatching noun contained within a modifier has an impact on error incidence: the greater the distance, the lower the error rate. The study presented in this paper investigated whether this distance effect is purely syntactic; if so, then it would be expected that there would be fewer errors following The owner of the house which charmed the realtors... than following The owner of the house who charmed the realtors..., since in the latter, the mismatch is syntactically nearer the head noun. Results show no hint of a difference between the two, suggesting that the distance effect is more likely due to temporal distance rather than syntactic distance per se.