SyntaxError: Non-UTF-8 code starting with '\x90' in

[x011]

I'm unable to extract the files contained on a exe build with pyinstaller 3.5.dev0+g19d8a378.mod.
Here's the error:

SyntaxError: Non-UTF-8 code starting with '\x90' in...exe

Is this a new protection from the latest pyinstaller or am I missing something?
Thank you.