In an embodiment, a fluid ejection device includes a thin-film layer formed over a substrate. A primer layer is formed over the thin-film layer, and a chamber layer is formed over the primer layer that defines a fluidic channel leading to a firing chamber. The fluid ejection device includes a slot that extends through the substrate and into the chamber layer through an ink feed hole in the thin-film layer. The fluid ejection device also includes a particle tolerant extension of the primer layer that protrudes into the slot. In some implementations, the particle tolerant primer layer extension extends across a full width of the slot.