1 files changed, 2 insertions, 1 deletions

diff --git a/lisp/progmodes/tcl.el b/lisp/progmodes/tcl.el
index 8f7705ba17d..e4e96554c95 100644
--- a/lisp/progmodes/tcl.el
+++ b/lisp/progmodes/tcl.el
@@ -1028,7 +1028,8 @@ Returns nil if line starts inside a string, t if in a comment."
     (with-current-buffer (process-buffer proc)
       ;; Delete prompt if requested.
       (when (marker-buffer inferior-tcl-delete-prompt-marker)
-        (delete-region (process-mark proc) inferior-tcl-delete-prompt-marker)
+        (let ((inhibit-read-only t))
+          (delete-region (process-mark proc) inferior-tcl-delete-prompt-marker))
         (set-marker inferior-tcl-delete-prompt-marker nil))))
   (comint-output-filter proc string))