diff --git a/fill3/fill3/terminal.py b/fill3/fill3/terminal.py
index d434a7d..fbd3b21 100644
--- a/fill3/fill3/terminal.py
+++ b/fill3/fill3/terminal.py
@@ -20,6 +20,7 @@ CTRL_DOWN = ESC + "[1;5B"
 CTRL_LEFT = ESC + "[1;5D"
 CTRL_RIGHT = ESC + "[1;5C"
 CTRL_SPACE = "\x00"
+CTRL_UNDERSCORE = "\x1f"
 ENTER = "\n"
 TAB = "\t"
 DELETE = ESC + "[3~"