During embryogenesis, the vertebrate hindbrain is segmented along its anteroposterior axis into lineage-restricted compartments, known as rhombomeres (r1-r8), that dictate subsequent neural patterning. The signals that pattern the hindbrain are known, but how each rhombomere-specific gene expression pattern is established is unclear. On p. 65, Sabine Cordes and colleagues reveal that the homeobox protein Cdx1 patterns the mouse hindbrain by spatially restricting the expression of the transcription factor MafB. Mafb is required for r5 and r6 development, and its expression is restricted to these segments. The authors report that the Mafb enhancer contains candidate Cdx-binding sites, and that Cdx1 binds to these sites both in vitro and in vivo. They show that Cdx1 is expressed at the r6/r7 boundary, at the posterior limit of the Mafb-expressing domain. Importantly, in the absence of Cdx1, MafB expression extends beyond its normal r6/r7 boundary. The authors propose that Cdx1 acts as an early and transient repressor of Mafb, and thus plays a role in refining hindbrain identity.