Dibromostyrene has a marked tendency to polymerize on storage. The induction period can be lengthened with the use of a stabilizing quantity of n-propylgallate. The induction period can be markedly prolonged when the gallate ester is admixed with phenothiazine, N,N,N',N'-tetramethyl-p-phenylenediamine, or 4-tert-butyl catechol.