I am receiving the #DIV/0! in a formula and would like to have "-" in place of it.

My basic formula is: =IF(A20=0,0, A20-A21)/A20

I would like it to =IF(A20=0,"-",A20-A21)/A20

I have tried nesting the "IF" and "ISERROR" but it is not working. Can someone please assist me.