Add a word to a string based on a conditional statement

I'm trying to add a word to the end of a string based on an ifelse statement and having trouble.

words <- c("one","two","one","four")
newword <- "word"

and then if the value equals "one", I want to append a word

words <- ifelse(words == "one",
            gsub(paste(newword,sep = " "),"",words),
            words)

I want the output to be

> words
[1] "one word"  "two"  "one word"  "four"

any idea why I can't make this happen with an ifelse and the paste() function?

Thanks for the help!