Buying selling property at same time , I need advice !!!!

I require advice. I am simultaneously selling one property and purchasing another. My solicitor recommends including clauses in the purchase contract allowing me to withdraw if the sale of my existing property isn't finalized within four weeks, as a form of self-protection. He wants me to sign the purchase contract today, before the sale of my existing property is complete; I've already paid a deposit. Is this the right course of action? Thank you.