Rollover traditional IRA with basis to qualifying tax deferred work plan (401K). Traditional IRA has a small amount of basis. What do I do with the basis amount?

I want to rollover all my traditional IRA to my qualifying tax deferred work plan (401K).  Traditional IRA has a small amount of non-tax deferred basis.  When I do the rollover to the tax deferred 401K, what do I do with the non-tax deferred basis amount?