stackheight is too large (threaded headset)

I don't have a front brake, so that won't happen.. I'll just try it like this, if the locknut will come off I will notice it and try thinking of a solution..
Untill then I'll just keep it like this.
Thanks for the replies!

You misunderstand. A front brake won't cause the headset to come loose, it will just throw up a nice clear symptom that it is loose. Do you have a rear brake by any chance?

Also, what ncjlee said.