从Golang中的JSON解析字符串以枚举

I have an enum defined as

type MyEnum int

const(
   FirstEnum MyEnum = iota
)

"Key": "FirstEnum"

var data map[string]interface{}
err := json.Unmarshal([]byte(json), &data)
x := data["key"].(MyEnum)

When I run this, however, I get the error:

panic: interface conversion: interface {} is string, not ps.Protocol [recovered]
        panic: interface conversion: interface {} is string, not ps.Protocol

Is there a way to get this to work like a normal conversion of a string representation of a enum to enum type in Go?