At about 7:09 p.m. Sunday, the man entered Foodies convenience store, at 9652 S. Pulaski Rd. in Oak Lawn, according to Oak Lawn police Cmdr. Randy Palmer.
"The clerk actually said, 'You're joking, right?' and the guy says,' No, I'm serious,'" Palmer said, according to the Chicago Tribune.
Wearing a mask depicting the "Nightmare on Elm Street" villain and carrying a "machete" in one hand and a large Bowie knife in the otheer, the man demanded money from the register and then ran away.
The robber was further described as as a white male between 37 and 43 years old. He was about 5 feet, 10 inches tall and weighed aobut 280 pounds, the clerk told police, clarifying that the man's skin color could be seen through the eye holes in the mask.
Along with the Freddy Krueger mask, the man was wearing a blue hoodie sweatshirt and khaki pants, Palmer said.
The clerk was the only one in the store at the time and was not injured.
No one is in custody.