diff --git a/jump-box/startup.bash b/jump-box/startup.bash
index 73f02d6..c3bbb68 100644
--- a/jump-box/startup.bash
+++ b/jump-box/startup.bash
@@ -1,5 +1,15 @@
 #!/bin/bash -e
 
+# Write an sshd_config.d drop-in with a HostKey line for each key in /etc/ssh/keys,
+# then exec any given command (e.g. /usr/sbin/sshd -D -e).
+set -euo pipefail
+shopt -s nullglob
+keys=( /etc/ssh/keys/ssh_host_*_key )
+(( ${#keys[@]} )) || { echo "no host keys in /etc/ssh/keys" >&2; exit 1; }
+mkdir -p "$(dirname "/etc/ssh/sshd_config.d/10-hostkeys.conf")"
+printf 'HostKey %s\n' "${keys[@]}" > "/etc/ssh/sshd_config.d/10-hostkeys.conf"
+
+# Setup the target user and their group
 echo "Setting up target user ${TARGET_USER} (uid=${TARGET_UID}, gid=${TARGET_GID})..."
 groupadd --gid "$TARGET_GID" "$TARGET_USER"