```ts
const MODULUS = 1000000007;

/**
 * The nth Fibonacci number, modulo 1000000007.
 */
export function fibMod(n: number): number {
  if (n < 0) {
    throw new Error("Input must be a non-negative integer");
  }
  
  let prev = 0;
  let curr = 1;
  for (let _ = 2; _ <= n; _++) {
    const temp = (prev + curr) % MODULUS;
    prev = curr;
    curr = temp;
  }
  
  return curr;
}
```