The Black Swan star admits she doesn't keep up with pop culture, but after hearing the hype about James' novels, she decided to approach the writer at a party - and now she wishes she hadn't.
She tells Britain's Red magazine, "This is how out of the loop I am. I met EL James at a party and I'd heard about the book so I knew everyone was talking about it, but because there's a tie on the cover I thought it was about Wall Street!
"I think I said something really stupid to her because I literally thought it was about the economy."
Ryder won't need to read the books to learn all about the racy story - Fifty Shades of Grey is currently being adapted for a film starring Jamie Dornan and Dakota Johnson and is slated for release in February, 2015.