Arithmetic overflow error when using DATEADD with [Timestamp] column in sys.dm_os_ring_buffers

Hello,

I'm trying to execute a SELECT query on the sys.dm_od_ring_buffers DMV in order to identify issues related to CPU contention that have been occurring for x number of minutes.  The error I'm receiving is:

Msg 8115, Level 16, State 2, Line 8
Arithmetic overflow error converting expression to data type int.

The expression causing the error is noted as follows:

dateadd(ms, - 1 * (@TimeNow - [timestamp]), GetDate()) EventTime 

(NOTE: @TimeNow uses the datatype BIGINT and it's value is set by converting the ms_ticks column in sys.dm_os_sys_info to FLOAT)

Any help is much appreciated.  I've tried casting this sucker every which way and I can't get around the overflow error.  Thanks!