According to People magazine, the ceremony is being put together at such short notice, guests are being called on the phone to give them a heads up about the invitations that will come in the mail.
Khloe found the perfect wedding band while ring shopping with Lamar last week and that made the couple decide to jump ahead and get married.
“She’s not wearing it yet because it is being re-sized," a source said.
Last week the couple reportedly decided to get engaged after “talking about rings”, but no one from either family would comment on the speculation.
However, 25-year-old Khloe’s older sister Kim recently said things were going well between Khloe and the hunky basketball player.
"They're very, very happy," Kim said. "She thinks he's amazing and he makes her laugh and smile constantly."
Lamar, 29, has two children - seven-year-old son Lamar Jr. and 10-year-old daughter Destiny - with ex-girlfriend Liza Morales.
Lamar and his ex also had a son, Jayden, who died from sudden infant death syndrome (SIDS) at seven months in 2006.