Mohammed Ben Fradj admitted the offence, which took place in the autumn last year, on Friday.
The Tunisian national will be sentenced before the Royal Court on 2 October.
Following Fradj’s guilty plea, Crown Advocate Emma Hollywood requested he be remanded in custody.
His lawyer, Advocate Adam Harrison, didn’t make an application for bail.
Fradj was already listed on the Sex Offenders’ Register regarding an indecent assault that took place in 2016.