Error: (void-function -filter)

[tjbrn]

In ‘fzf’ source: ‘helm-fzf--do-candidate-process’ 
 (void-function -filter)

Is -filter correct in helm-fzf--do-candidate-process?
The error disappeared after changing it to seq-filter.

My minimal init.el:

;; setup melpa and use-package
...

(use-package helm
  :ensure s
  :ensure t)

;; only helm-fzf.el are being loaded
(cl-loop for file in (directory-files "~/.emacs.d/config" t)
         when (string-match "\\.el$" file)
         do (load file))

Arch
Emacs 25.3.1