A mutation causing self‐fertility (SF) in perennial ryegrass (Lolium perenne L.) was studied at the tetraploid level. The aim of this work was to determine a) whether SF remains functional in a tetraploid population; and b) if the SF mutation expresses dominance in heterozygous pollen grains. A tetraploidized plant carrying SF alleles was self‐pollinated to create a segregating F2 population. In the F2 individuals, pollen compatibility ranged between 38% and 84% showing that SF remained functional. The SF locus genotype was the main determinant of pollen compatibility explaining 78% of the variation. The observed segregation was significantly different from the expected under both SF being dominant or recessive models (P(χ2)≤0.001), and tended to be intermediate between them, indicating partial dominance or additive gene action. The frequency of the different genotypes suggested that pollen grains homozygous for the mutation have a competitive advantage over heterozygous pollen and that pollen compatibility is affected by the interaction with additional loci. The implications of our results for breeding polyploid grasses are discussed.