Gradle: A problem occurred configuring project

Weird error message:

Gradle: A problem occurred configuring project ':App'.
> Failed to notify project evaluation listener.
   > Could not resolve all dependencies for configuration ':App:_DefaultFlavorDebugCompile'.
      > Could not find any version that matches com.android.support:appcompat-v7:+.
        Required by:
            MyApplication:App:unspecified

If this happens, just go to Tools -> Android -> Android SDK Manager, then check “Android Support Repository” and “Android Support Library” under “Extra” and install them. That should take care of the error.