The histone methyltransferase SUV39H1 trimethylates histone 3 at Lys9 (H3K9me3), which represses gene expression. Here, the authors find that SUV39H1 is targeted by the tumour suppressor p53. Specifically, the authors observed that p53 represses SUV39H1 expression through two of its targets, p21 (which represses SUV39H1 at the transcriptional level) and the E3 ubiquitin ligase MDM2 (which promotes SUV39H1 degradation). So why does p53 target SUV39H1? The authors found that the H3K9me3 mark was present on the promoters of p53 target genes but that it decreased after p53 induction. Moreover, overexpression of SUV39H1 inhibited p53-dependent cell fate decisions — cell cycle arrest and apoptosis — and SUV39H1 silencing enhanced p53-dependent apoptosis. Together, these findings reveal that p53 represses SUV39H1 to promote the expression of its target genes.