now, sure as the sun will cross the sky, the fly is open.

The story:

my husband was absentmindedly singing this to our daughter as she was getting ready for bed. i overheard his correct version and asked him if he was sure it was right. then i told him what i'd always thought the lyrics were. he laughed a lot and was also incredulous. now we sing my lyric at home cuz it's a big improvement on a song that could use some help.