Regex character repeats n or more times in line with grep

I need to find the regex expression to find a character that repeats 4 or more times with grep.

I know that the expression is {n,}, so if I need to find lines, for example, when the character "g" repeats 4 or more times, in theory with grep man page is:

grep "g{4,}" textsamplefile

But doesn't work. Any help?