diff --git a/oni-core.el b/oni-core.el
index dbea8c3..212d126 100644
--- a/oni-core.el
+++ b/oni-core.el
@@ -4,7 +4,7 @@
 
 ;; Author: Tom Willemse <tom@ryuslash.org>
 ;; Keywords: local
-;; Version: 2020.0407.015402
+;; Version: 2020.0407.212814
 ;; Package-Requires: (oni-data-dir expand-region multiple-cursors embrace helpful)
 
 ;; This program is free software; you can redistribute it and/or modify
@@ -35,6 +35,9 @@
 
 (defalias 'yes-or-no-p 'y-or-n-p)
 
+(defvar oni-core--recentf-idle-timer nil
+  "Internal variable keeping track of a timer started for ‘recentf-save-list’.")
+
 (defun oni-core--destroy-trailing-whitespace ()
   "Delete trailing whitespace everywhere, except in Markdown buffers."
   (if (not (eq major-mode 'markdown-mode))
@@ -144,7 +147,9 @@
 (global-set-key (kbd "C-<left>") 'winner-undo)
 (global-set-key (kbd "C-<right>") 'winner-redo)
 
-(run-with-idle-timer 10 t 'recentf-save-list)
+(unless oni-core--recentf-idle-timer
+  (setq oni-core--recentf-idle-timer
+        (run-with-idle-timer 10 t 'recentf-save-list)))
 
 (electric-indent-mode -1)
 (winner-mode)
diff --git a/test/oni-core-test.el b/test/oni-core-test.el
index 0672fb3..eb9886e 100644
--- a/test/oni-core-test.el
+++ b/test/oni-core-test.el
@@ -59,3 +59,12 @@
     (oni-core-move-end-of-dwim)
     (oni-core-move-end-of-dwim)
     (should (equal 21 (point)))))
+
+(ert-deftest oni-core-loading-is-idempotent-recentf-idle-timer ()
+  "Test that loading ‘oni-core’ is idempotent in regards to an idle timer."
+  ;; We already loaded it with the ‘require’ call above. We load it again so we
+  ;; can check that the timer set up in it doesn’t appear twice.
+  (load-library "oni-core")
+  (let* ((pred (lambda (elt) (eq 'recentf-save-list (aref elt 5))))
+         (matches (delete nil (mapcar pred timer-idle-list))))
+   (should (eq 1 (length matches)))))