How to keep straw inside coop from being kicked out pop door?

[My Three Chicks]

My girls keep kicking out a bunch of straw from inside the coop out the auto door into the Run.

Is there something I can build or do to keep it inside the coop and not spill out anywhere?

See pics

 

[nuthatched]

Raise the door or add a threshold

 

[aart]

Screw a 1x6 board to the 2x2 vertical framing on the sides of the door.