no sea que
conjunctionCEFR B1
What does “no sea que” mean in English?
lest, in case
lest, in case (no sea que + subjunctive — precautionary purpose, always subjunctive)
Example sentences
Lleva el cargador, no sea que se te acabe la batería durante el vuelo.
Take the charger in case your battery dies during the flight.
Guarda una copia de seguridad del archivo, no sea que el ordenador se cuelgue antes de terminar.
Save a backup of the file in case the computer crashes before you finish.
Salimos una hora antes, no fuera a ser que hubiera atascos en la autopista por las obras.
We left an hour early in case there were traffic jams on the motorway because of the roadworks.
How to use it
No sea que means 'lest' or 'in case / for fear that' — it introduces a precautionary purpose clause and always triggers subjunctive. 'Lleva paraguas, no sea que llueva' (Take an umbrella in case it rains). It expresses that the main action is taken as a precaution against an undesired outcome. An extended variant 'no vaya a ser que' is also common in colloquial speech and means the same thing. Both always take subjunctive.
Common mistake
No sea que is always followed by subjunctive — it is essentially a purpose conjunction expressing fear of an undesired outcome. Do not confuse it with 'a menos que' (unless) or 'en caso de que' (in case) — while related in meaning, no sea que has a stronger precautionary/preventative flavour. 'No vaya a ser que' is the colloquial extended form meaning the same thing.