Double Square Puzzle

This is a novel puzzle. 
You hand over four cut out pieces to a spectator to form into a perfect square.
This is relatively easy, and the spectator will form the square with a few attempts.
But as an afterthought you hand him another piece, - a small square.

Now ask him to form a perfect square using all five pieces. This will prove much more difficult, till you demonstrate how easy it is.
The solutions for forming the square with the four (and five) pieces supplied are illustrated for you.