slime-edit-definition doesn't lookup the definition at point

In my Lisp buffer, when the point is over a symbol and I press M-.
(slime-edit-definition), I get the following error:

    cl-assoc: Symbol's function definition is void: equalp

If the point is over some whitespace, then things work as expected:
M-. gives me the "Edit Definition of" prompt in the minibuffer and
looks up the correct definition.

I guess I can define equalp in my .emacs to fix this, but I would
prefer if it worked out of the box.

I am using GNU Emacs 24.5.1 and SLIME 20160624.851 (installed from melpa).

Chaitanya