The man walked into the store on Belmont and Chestnut just before 1 am and pulled a gun on the clerk.
Investigators say he told the clerk to give him money from both registers. That's when two customers walked into the store.
"They entered the store as the robbery was going on. This obviously caught the suspect's attention, and the suspect exited the store and then ran southbound on Chestnut from Belmont," said Fresno Police Lt. Sean Biggs.
No one was hurt.
Police say the suspect is 4'10" tall with a thin build. He was dressed in all black, wearing a hoodie sweatshirt, ski mask, and black shoes.