String popping out of the nut

[GeneralElectric]

I've got a fretless P bass where one of its strings broke. The only set I had lying around were Black Beauties. (45-105) I think the old ones were the same gauges.

Anyways, the A string keeps popping out of the nut. It keeps sliding out and going to the bass side right next to the E.

The nut cut itself looks kinda shallow. Maybe thats it?

[202dy]

It could be insufficient back pressure (down angle) at the nut. Make sure the string is wound from the top to the bottom of the peg. That will give sufficient down angle to keep the string in the slot.

[PBass101]

If all else fails, take it to a pro.