Brooks tension nut slipping

[gom]

The tension nut on my road bike’s B17 slowly turns under tension - and my weight - resulting in excessive sagging.
Any tips to stop this?

 

[Cycleops]

You need some Loctite.

 

[themosquitoking]

Is there room there for a locknut?

 

[Gazjacko]

Are you sure it’s not the ‘nose’ piece moving? They can splay open with time and mess up your saddle tension. A gentle squeeze in a wood vice sorts it