Donnacha O'Brien admitted to "an oversight" which came at a cost of a seven-day suspension at Galway on Friday evening.
O'Brien received the ban after he "attempted to weigh out without the harness attachment on his back protector" prior to riding Queen Iseult in a mile-and-a-half fillies' maiden.
Queen Iseult finished fourth behind Lure Of The Sea.
Galway's stewards said in a statement that they "considered his clean record", but O'Brien was still suspended for seven days.
The young rider is currently leading the standings in the race to be crowned Irish Flat champion jockey.
Reigning champion Colin Keane is his nearest pursuer.