Is 401K employee contribution limit separate for income from an employer and income from self-employment? In other words, is it 18K combined or 18k for each income source

I was under the assumption that employee 401K contribution limit is $18K total for income from ALL sources. I have entered a W2 with $11K of deferred income to an employer's 401K plan. As the same time, Turbo Tax allows me to have the maximum 401K contribution of $53K ($18K employee + $35K employer). Is this correct?