--- a/lisp/erc/erc.el
+++ b/lisp/erc/erc.el
@@ -2052,9 +2052,10 @@ defun erc-initialize-log-marker (buffer)
   "Initialize the `erc-last-saved-position' marker to a sensible position.
 BUFFER is the current buffer."
   (with-current-buffer buffer
-    (setq erc-last-saved-position (make-marker))
-    (move-marker erc-last-saved-position
-                 (1- (marker-position erc-insert-marker)))))
+    (unless (markerp erc-last-saved-position)
+      (setq erc-last-saved-position (make-marker))
+      (move-marker erc-last-saved-position
+                   (1- (marker-position erc-insert-marker))))))
 
 ;; interactive startup