Maven+Eclipse: Unbound classpath variable M2_REPO

Got "Unbound Classpath Variable M2_REPO" in Eclipse? It's because M2_REPO system variable is not added to eclipse classpath. How to fix this?

1. Open eclipse
2. Window -> Preferences 
3. Java -> Build Path -> Classpath Variables -> New
4. Name: M2_REPO
5. Path: browse to the .m2/repository folder