Some friendly advice for pop stars: do some research before giving private concerts!

Mariah Carey is receiving heavy criticism after performing a two-hour concert for authoritarian Angolan President José Eduardo Dos Santos, five years after she gave a performance for Libyan dictator Muammar al-Gaddafi.

The superstar reportedly received a sum of $1 million for the concert, which has angered human rights groups who claim that Dos Santos has murdered many of his own people and exploited the country’s resources.

“It is the sad spectacle of an international artist purchased by a ruthless police state to entertain and whitewash the father-daughter kleptocracy that has amassed billions in ill-gotten wealth while the majority of Angola lives on less than $2 a day,” Human Rights Foundation president Thor Halvorssen said.

Unitel, a mobile-phone company owned by Dos Santos’ daughter Isabel, reportedly sponsored the concert.

Halvorssen added, “Mariah Carey can't seem to get enough dictator cash. Just five years ago she performed for the family of Libyan dictator Muammar al-Gaddafi.

“Now, she goes from private performances to public displays of support and credibility for one of Africa's chief human rights violators and most corrupt tyrants.”

Carey apologized for her al-Gaddafi performance in 2011, the same year the dictator was toppled and killed during the Arab Spring uprising.

At the time, she released a statement that read, “I was naive and unaware of who I was booked to perform for. I feel horrible and embarrassed to have participated in this mess.”

Photos have since been released of the “#Beautiful” singer posing with the Dos Santos family.

Carey isn’t the first celebrity to find herself in hot water for giving a private performance.

Six months ago, Jennifer Lopez apologized for serenading Turkmenistan dictator Gurbanguly Berdimuhamedow, whose government is accused of arresting and torturing political opponents.

And Gaddafi was notorious for booking popular U.S. stars for his parties including Nelly Furtado in 2007 and Beyoncé and Usher for a party thrown by his son in 2010.

Hopefully this second incident will really teach Carey a lesson.