diff --git a/lib/openmsx/share/scripts/fail_after.tcl b/lib/openmsx/share/scripts/fail_after.tcl
index 8ea3fdd..6ac9783 100644
--- a/lib/openmsx/share/scripts/fail_after.tcl
+++ b/lib/openmsx/share/scripts/fail_after.tcl
@@ -40,7 +40,10 @@ proc fail_after { timeout {time_unit "time"} {fail_id "fail_after"} {fail_code 2
 	global fail_after_prev_id
 	set msg ""
 	if {$fail_after_prev_timer != 0} {
-		after cancel $fail_after_prev_timer
+		if {[catch {after cancel $fail_after_prev_timer} err_msg]} {
+			puts stderr "error: $err_msg"
+			fail_after_exit fail_after_cancel_error 1
+		}
 		set msg "mb::fail canceled $fail_after_prev_id"
 	}
 	set fail_after_prev_id $fail_id