diff --git a/tools/xen/scripts/on_exit.sh b/tools/xen/scripts/on_exit.sh
index 2441e3d84a..2846dc42d0 100755
--- a/tools/xen/scripts/on_exit.sh
+++ b/tools/xen/scripts/on_exit.sh
@@ -3,7 +3,9 @@
 set -e
 set -o xtrace
 
-declare -a on_exit_hooks
+if [ -z "${on_exit_hooks:-}" ]; then
+    on_exit_hooks=()
+fi
 
 on_exit()
 {