'frequency_t' has not been declared

Hi, i got a problem with this code (sorry for my english)

I'm triying to declare this enum at the beginning of the program

enum frecuency_t { CLK_1MHZ, CLK_2MHZ, CLK_2DOT5MHZ, CLK_4MHZ, CLK_NO_CLK};

and when i tried to use it in the next lines

uint16_t activate(uint8_t* buf, uint16_t buf_size, frequency_t frequency=CLK_1MHZ); inside of a class

says that error

i've been triying to put inside the class but it's the same
whan i'm doing wrong?

is it :

frecuency_t

or

frequency_t

?