diff --git a/lisp/ansi-color.el b/lisp/ansi-color.el
index c329bab5788..ce84af445a5 100644
--- a/lisp/ansi-color.el
+++ b/lisp/ansi-color.el
@@ -86,6 +86,8 @@
 
 ;;; Code:
 
+(defvar comint-last-output-start)
+
 ;; Customization
 
 (defgroup ansi-colors nil