Madrid, Spain (CNN) -- An African man who claimed he could double your money simply by applying a magic potion to currency notes has been arrested at a Madrid bar where the Ecuadorean owner nearly fell victim to the ploy, Spanish national police said on Thursday.

Police arrived in time to catch the suspected thief, from Cameroon, with 1,120 euros ($1,556) that had been handed over by the bar owner. The suspect, 28, alleged he had run out of magic potion and would need to go home to get some more, a police statement and spokesman said.

"It was a very unpleasant surprise," bar owner Cesar Tepan told CNN.

He told police the suspect had come to the bar a week earlier claiming he could double currency notes by applying a magic potion, the police statement said.

Taking a chance, the owner provided a 20 euro note (nearly $28), and the suspect mixed it with various white papers, applied a brown liquid and white power, and mixed it up with cotton. Presto, and there were soon three 20 euro notes visible, the owner told police.

"He returned my 20," said Tepan, who's lived 16 years in Spain and has owned the bar in central Madrid for 11 years.

When the suspect came back last Saturday, the owner provided 1,120 euros in various currency notes, after the owner and the suspect agreed on how to split up the proceeds from the doubled money, the police said.

The suspect put the bills in an envelope and sealed it with tape. Then he applied the alleged magic potion, repeating this various times, but finally told the bar owner he had run out of the magic potion and would need to go home and get more.

But he promised to leave the sealed envelope at the bar. That's when an argument ensued and someone, possibly the owner or a client, called the police, a police spokesman said.

"I realized he was trying to take the money," Tepan told CNN. A neighbor called the police and Tepan's adult son arrived and locked the door to the street, with the suspect inside the bar.

"He became nervous," Tepan said, adding he was determined not to let the suspect leave until the 1,120 euros had been returned.

The police arrived and opened the sealed envelope but found only white papers inside. Then they searched the suspect, and found the 1,120 euros hidden in his clothing, the police statement said.