Macro Runs On Wrong Workbook On Close

I have a macro on a particular workbook that runs when the workbook closes.

This runs fine when I close the workbook itself. If I happen to have other workbooks open and then I close EXCEL rather than an individual workbook, my macro that runs on close always runs when it is not the active workbook.

To put it another way, say that my 'run on close' macro is workbook 1. I also have workbooks 2 and 3 open as well. If workbook 3 is the active workbook and I choose to close Excel (and thus close all three workbooks), my 'run on close' macro runs straight away and, worse still, will run it on workbook 3 (my active workbook).

How can I stop the macro running until it is the active workbook in the closing chain, so that it only runs on the correct workbook? (workbook 1 in my example)