rng.Lock()
	defer rng.Unlock()

	randomInt63 := rng.rand.Int63()
	remaining := maxAlphanumsPerInt
	for i := 0; i < n; {
		if remaining == 0 {
			randomInt63, remaining = rng.rand.Int63(), maxAlphanumsPerInt
		}
		if idx := int(randomInt63 & alphanumsIdxMask); idx < len(alphanums) {
			b[i] = alphanums[idx]
			i++
		}
		randomInt63 >>= alphanumsIdxBits
		remaining--
	}
	return string(b)