Golang random 64-bit integer from crypto/rand

I want to generate 64-bit random integer using the secure crypto/rand package. I found this online:

package main

import (
    "crypto/rand"
    "encoding/base64"
)

// GenerateRandomBytes returns securely generated random bytes.
// It will return an error if the system's secure random
// number generator fails to function correctly, in which
// case the caller should not continue.
func GenerateRandomBytes(n int) ([]byte, error) {
    b := make([]byte, n)
    _, err := rand.Read(b)
    // Note that err == nil only if we read len(b) bytes.
    if err != nil {
        return nil, err
    }

    return b, nil
}

But it seems to generate random bytes instead. I want a random 64-bit int. Namely, I want something like var i uint64 = rand(). Any ideas how to achieve this?