I testify to everyone who hears the words of prophecy in this book: If anyone adds to them, God will add to him the plagues described in this book.
KJV
For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book:
ASV
I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto them, God shall add unto him the plagues which are written in this book: