Can's submit line breakpoint if another class with same name and package exists

Not able to submit breakpoint LineBreakpoint Main.java : 7, reason: Breakpoint's source file does not belong into the preferred source root 'C:\path\to\other\project\src\main\java'.
See Window/Debugging/Sources and assure that the intended source roots are selected for debugging.
Invalid LineBreakpoint Main.java : 7

package my.package;

public class Main {

    public static int foo() {
        int i = 3;
        i++;
        return i;
    }
}