I don't know where you got that regex from, but it's certainly not from japhy's code. The regex his code produces is: (?-xism:^[^pcd]*(?:(?:p(?!ig)|c(?!at)|d(?!og))[^p c d]*)*$) (That's also the regex you used in your earlier response.) The regex you used in your latest response has a parenthesis in the wrong place and is missing a quantifier; of couse it doesn't work!