Index: sys/boot/forth/menu.4th
===================================================================
--- sys/boot/forth/menu.4th	(revision 264244)
+++ sys/boot/forth/menu.4th	(working copy)
@@ -897,10 +897,10 @@ create kernelsbuf 256 allot
 
 				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)
 
-					s" menu_timeout_command"  getenv dup
+					s" menu_timeout_command" getenv dup
 					-1 = if
 						drop \ clean-up
 					else
@@ -915,10 +915,17 @@ create kernelsbuf 256 allot
 			( -- )
 		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 !
@@ -927,14 +934,9 @@ create kernelsbuf 256 allot
 				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