The present invention relates to a method for depositing a zinc-nickel alloy on a substrate, particularly to a method for electrolytically depositing a zinc-nickel alloy on a substrate, wherein a zinc-nickel deposition bath is utilized as a catholyte comprising at least one brightening agent, wherein the at least one brightening agent has a source which is substantially free of, preferably does not comprise, halogen anions. The present invention furthermore relates to a respective aqueous zinc-nickel deposition bath, a respective brightening agent, and a respective use of said brightening agent for replenishing in an aqueous zinc-nickel deposition bath.