C# - Compare listboxes - remove listbox item from listbox1 if it does not exist in listbox2

I'm trying to use the below but it's spitting out an error and won't work.

The error I'm receiving is:

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Windows.Forms.dll

Additional information: List that this enumerator is bound to has been modified. An enumerator can only be used if the list does not change.

            foreach (string i in listbox1.Items)
            {
                if (!listbox2.Items.Contains(i))
                {
                    listbox1.Items.Remove(i);
                }
            }

Any help would be greatly appreciated.

Thanks