It’s incorrect to state that indentured servants were the same as slaves. An indentured servant signed a contract to work for a period of time in exchange for something; often passage to America, clear a debt, etc. Once the terms of the contract was met the indentured servant was a free man.
The term of indenture was frequently ignored. The first black slave of Anthony Johnson had been an indentured servant. He was held by Anthony for years past his freedom date.