diff --git a/extensions/legit/legit-rebase.lisp b/extensions/legit/legit-rebase.lisp
index 91262c8f1..d851b7c08 100644
--- a/extensions/legit/legit-rebase.lisp
+++ b/extensions/legit/legit-rebase.lisp
@@ -40,6 +40,11 @@ and
      :keymap *legit-rebase-mode-keymap*)
   (setf (variable-value 'enable-syntax-highlight) t))
 
+(define-file-associations legit-rebase-mode
+  ((:file-namestring "git-rebase-todo")
+   (:file-namestring "git-rebase-todo.backup")))
+
+
 ;; Use commits with a keypress:
 (define-key *legit-rebase-mode-keymap* "p" 'rebase-mark-line-pick)
 (define-key *legit-rebase-mode-keymap* "r" 'rebase-mark-line-reword)
diff --git a/src/file.lisp b/src/file.lisp
index 24ab35233..9a221dcd7 100644
--- a/src/file.lisp
+++ b/src/file.lisp
@@ -12,6 +12,21 @@
   (get mode 'file-mode-associations))
 
 (defmacro define-file-associations (mode specs)
+  "Associate a mode to a list of file names so that the files are always open in this mode.
+
+  Specs are in the form (:spec \"filename\"),
+
+  Available specs:
+
+  :file-namestring
+
+  Example:
+
+  (define-file-associations makefile-mode
+    ((:file-namestring \"Makefile\")
+     (:file-namestring \"makefile\")))
+
+  See also DEFINE-FILE-TYPE."
   `(setf (file-mode-associations ',mode) ',specs))
 
 (defun get-file-mode (pathname)