On a theorem of camillo

Let R denote a right principally injective ring. In this note we show that if R is right duo then R is right finite dimensional if and only if R has a finite number of maximal left ideals. This extends and answers an open question of Camillo. If, instead, every simple right module can be embedded in R, we show that R is left finite dimensional if it has a finite number of maximal right ideals.