Using a 1333Mhz DDR3 in my 1600Mhz DDR3 laptop

[zakariasalem5]

Hi.
I tried looking for solutions but i couldnt find any.
I have a new asus notebook, and it has 4GB DDR3 1600Mhz ram and an empty slot.
I want to add more ram i got an extra 4GB DDR3 1333Mhz ram laying around.
What would happen if i just add it in the second slot?
My laptop is Asus X456U i5 variant.
Thanks in advance!

 

[CountMike]

If it works at all, faster one will run at speed of slower one.