Emacs freezes when autocompleting for lisp prompt

[JacobDFisher]

I'm running emacs 24.5.1 on ubuntu mate 15.10, and emacs is freezing when a word in a lisp prompt is autocompleted. The code I am using to prompt for input is taken from gigamonkeys' Practical Common Lisp and is as follows:

(defun prompt-read (prompt)
(format query-io "~a: " prompt)
(force-output query-io)
(let ((response (read-line query-io)))
(if (not (equal response "")) response)))

While it is frozen, hovering over the various fields still causes them to be outlined; however, clicking does nothing. In addition, attempts to close it simply do nothing, and I have to kill the process to close emacs. Screenshot attached; though, I don't know how much that will help. Also, all the style-warnings are just saying that a function which I still have at the end of my code hadn't been defined when it was called.