Factual error: In the sequence set in 1740 during the battle a modern wooden park bench can be seen outside the castle. (00:44:30)
Continuity mistake: When Fiona and Paul first go inside the castle and rescue the professor from his time machine, they are standing talking to the prof. Fiona is on the left and Paul is on the right. The angle changes, and Paul and Fiona have swapped places. Another angle change, and Fiona and Paul are back in their original positions.
Audio problem: In the 1741 sequence When Sniffy Kemp grabs Fiona she screams, but her mouth does not move.
Factual error: In the dark ages sequence during the trial of the witches a row of electricity pylons can be seen in the distance.
Factual error: In the 1953 scene the Morris Oxford parked in a driveway is a 1957 model.
Continuity mistake: In the final scene when Paul gets the lacrosse team to get off the coach, when the camera is inside the coach two girls are off first, followed by the lady teacher. When the camera switches to outside of the coach the same two girls are out of the coach door first but the lady teacher is no where to be seen, and her place is taken by a schoolgirl.
Factual error: In the 1953 sequence the schoolboys in the changing room all have mullet hairstyles that were current when this film was made in 1978, but not for the setting.
Factual error: In the 1953 sequence when the headmaster is driving Fiona and Paul home, the yellow car parked in the road is a Vauxhall Viva HC, which didn't start production until 1970.
