```
import { abs } from 'mathjs';

const MODULUS = 1000000007;

export function fibMod(n: number): number {
  if (n < 0 || !Number.isInteger(n)) {
    throw new Error('n must be a non-negative integer');
  }

  let a = 0;
  let b = 1;

  for (let i = 2; i <= n; i++) {
    [a, b] = [b, (a + b) % MODULUS];
  }

  return b;
}
```