React useEffect runs twice on mount in development — is my data being fetched twice?

My useEffect is firing twice on component mount and I am seeing two API calls in my network tab. My component looks like this:

useEffect(() => {
  fetch('/api/data')
    .then(res => res.json())
    .then(setData);
}, []);

This is causing a duplicate entry in my database because the API writes a record on every call. Is this a bug in React 18 or am I doing something wrong?

Environment:

• React 18.2
• Create React App (development mode)
• No custom StrictMode setup