What kind of surface are you working it on?
There shouldn't be much of a problem on carpet because of the friction but I've worked it fine in the garage on cement. Wood floors might be a bit more tricky.
If you find your hands slipping, you might want to:
1. spread your fingers out to cover as much surface area as possible and grip the floor with the tips of your fingers as you normally would in a handstand
2. actively push your shoulders away from the floor. "Make your handstand taller". The pressure may help you not just slide away onto your head.
3. Put something soft underneath your head. I can generally roll out or step to the side when doing these off the wall and roll out when pressing to them. At home I do these on my futon mattress. Kind of flexes the wrists more than I'd like but it's softer and quieter so the roommates don't suspect I'm doing HS in my room.