diff --git a/lisp/simple.el b/lisp/simple.el
index 228ff1b350b..69b72639d97 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -2868,6 +2868,11 @@ for `auto-fill-function' when turning Auto Fill mode on."
 (defun turn-on-auto-fill ()
   "Unconditionally turn on Auto Fill mode."
   (auto-fill-mode 1))
+
+(defun turn-off-auto-fill ()
+  "Unconditionally turn off Auto Fill mode."
+  (auto-fill-mode -1))
+
 (custom-add-option 'text-mode-hook 'turn-on-auto-fill)
 
 (defun set-fill-column (arg)