Workers at a warehouse in Seine-et-Marne were no doubt shocked to discover ropes dangling from the ceiling of their building on Monday morning.
Realizing they'd been robbed, they alerted police.
A total of 75 boxes of postage stamps were reported missing, believed to have been hauled up through the roof by thieves on Sunday night.
An inventory is still being carried out, but their estimated haul is valued at €1.4 million, a police source told French newspaper L'Express.
The source added that CCTV footage from the scene was being examined.
The theft marks the second high-profile hit of its kind this year, after thieves almost got away with €20 million worth of stamps in February. Their haul was found by police in an abandoned vehicle by the roadside just hours after the heist.