Regex unknown modifier '[' in validation

I have this validation:

validate: "regex:/^[0-9A-F]+\/[0-9A-F]+$/"

So I have escaped the slash in the middle of the regex. But I get the error:

Regex unknown modifier '[' in validation

If it take out the \/ from the regex I don't get the error (but of course I need it there :-) ).

Thanks in advance.