Revealing mistakes: When Gerbier is being taken to the concentration camp at the beginning of the film, and the guard driving the police van makes an unexpected stop at the house, it is clear that the rain is only falling in front of the camera and directly on the van. Only a few feet away, there are no raindrops hitting the mud or the puddles of water.
Anachronisms: In the London WWII sequence, we see double yellow lines on the road. These were only introduced in the UK in 1956 and didn't become common until the 1960s. Same goes for a couple of the street signs, of a style not known before the 1960s.
Factual errors: In the end, it says "dimanche 23 février 1943" (Sunday, 23rd February, 1943) even though it was a Tuesday.
Continuity: In the sequence when Mathilde exits the car and silently waves goodbye to Gerbier, in response he rolls his window up completely, yet in the very next shot his window remains open as the car drives away.