```typescript
const MODULUS = 1000000007;

/**
 * The nth Fibonacci number, modulo 1000000007.
 */
export function fibMod(n: number): number {
  if (n < 0 || n % 1 !== 0) {
    throw new Error('n must be a non-negative integer');
  }

  let pre = 0;
  let cur = 1;

  for (let i = 2; i <= n; i++) {
    const tmp = (pre + cur) % MODULUS;
    pre = cur;
    cur = tmp;
  }
  return cur;
}
```