diff -u original/menu.4th new/menu.4th
--- original/menu.4th	2014-06-04 17:21:20.137501000 +0900
+++ new/menu.4th	2014-06-04 17:43:32.100160000 +0900
@@ -681,8 +681,8 @@
 
 				menu_timeout @ 0= if
 					\ We've reached the end of the timeout
-					\ (user did not cancel by pressing ANY
-					\ key)
+					\ (user did not cancel by pressing
+					\ ASCII sequence 0x8 BS or higher)
 
 					str_menu_timeout_command getenv dup
 					-1 = if
@@ -699,10 +699,17 @@
 			( -- )
 		then
 
-		key? if \ Was a key pressed? (see loader(8))
+		key? if ( and ) key dup 7 > if
 
-			\ An actual key was pressed (if the timeout is running,
-			\ kill it regardless of which key was pressed)
+			( -- N )
+
+			\ Was a key pressed? (see loader(8))
+			\ ... and was it a usable ASCII sequence?
+
+			\ NB: Some systems may generate ASCII 0x7 BEL when a
+			\ keyboard is not connected (e.g., booting serial)
+
+			\ If the timeout is running, kill it
 			menu_timeout @ 0<> if
 				0 menu_timeout !
 				0 menu_timeout_enabled !
@@ -711,14 +718,9 @@
 				0 menu-timeout-update
 			then
 
-			\ get the key that was pressed and exit (if we
-			\ get a non-zero ASCII code)
-			key dup 0<> if
-				exit
-			else
-				drop
-			then
-		then
+			exit
+
+		else drop then then
 		50 ms \ sleep for 50 milliseconds (see loader(8))
 
 	again