Looking on the internet deeply has found these results:

be careful not to lose is the most popular phrase on the web.

be careful to not lose 175,600 results on the web	be careful not to lose 12,510,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Be careful not to lose your 10000 francs... I have to be careful not to lose my footing. From now on, we must all be careful not to lose the King's love, or everything is lost. We have to be careful not to lose the emotion. You just got to be careful not to lose your separate selves along the way. Be careful not to lose his job. Be careful not to lose your soul. Earlier, I heard one speaker say that we must be careful not to lose our citizens.	I have to be careful not to lose my footing. Be careful not to lose your 10000 francs... Be careful not to lose your soul. Earlier, I heard one speaker say that we must be careful not to lose our citizens. From now on, we must all be careful not to lose the King's love, or everything is lost. We must therefore be careful not to lose sight of our responsibilities to Central Asia simply because we wish to strengthen relations with countries adjacent to the EU to its immediate east. You just got to be careful not to lose your separate selves along the way. We have to be careful not to lose the emotion.

be careful to not lose

175,600 results on the web

be careful not to lose

12,510,000 results on the web

More popular!

Be careful not to lose your 10000 francs...
I have to be careful not to lose my footing.
From now on, we must all be careful not to lose the King's love, or everything is lost.
We have to be careful not to lose the emotion.
You just got to be careful not to lose your separate selves along the way.
Be careful not to lose his job.
Be careful not to lose your soul.
Earlier, I heard one speaker say that we must be careful not to lose our citizens.

I have to be careful not to lose my footing.
Be careful not to lose your 10000 francs...
Be careful not to lose your soul.
Earlier, I heard one speaker say that we must be careful not to lose our citizens.
From now on, we must all be careful not to lose the King's love, or everything is lost.
We must therefore be careful not to lose sight of our responsibilities to Central Asia simply because we wish to strengthen relations with countries adjacent to the EU to its immediate east.
You just got to be careful not to lose your separate selves along the way.
We have to be careful not to lose the emotion.