A portable toilet has a cabin, a water closet in the cabin, a light-transmitting roof upwardly closing the cabin and having an outer edge, and a vent pipe projecting upward through the roof. A light fixture for the toilet has a housing adapted to fit in an installed position against an outer face of the roof and having a throughgoing hole fittable over the vent pipe and a side turned toward the roof. A light source in the housing is energizeable to emit light from the side through the roof and into the cabin. A latch formation on the housing is engageable with the rim to secure the housing to the roof.