diff --git a/Makefile b/Makefile
index dca12f5..8f304a3 100644
--- a/Makefile
+++ b/Makefile
@@ -34,8 +34,7 @@ root_overlay/bin/door.py: door_control/door.py
 	cp $< $@
 
 root_overlay/etc/dropbear/dropbear_ecdsa_host_key:
-	mkdir -p `dirname $@`
-	ssh-keygen -t ecdsa -f $@
+	sh -c 'if [[ ! -f $@ && ! -f $@.openssh ]]; then mkdir -p `dirname $@` && ssh-keygen -t ecdsa -f $@.openssh; fi'
 
 root_overlay/etc/wpa_supplicant/wpa_supplicant.conf:
 	mkdir -p `dirname $@`
@@ -51,4 +50,4 @@ clean:
 menuconfig:
 	make -C buildroot menuconfig
 
-.PHONY: all clean sdcard.img menuconfig root_overlay
+.PHONY: all clean sdcard.img menuconfig root_overlay root_overlay/etc/dropbear/dropbear_ecdsa_host_key
diff --git a/root_overlay/etc/init.d/S40dropbearkey.sh b/root_overlay/etc/init.d/S40dropbearkey.sh
new file mode 100644
index 0000000..b8deb28
--- /dev/null
+++ b/root_overlay/etc/init.d/S40dropbearkey.sh
@@ -0,0 +1,2 @@
+#!/bin/sh
+[[ ! -f /etc/dropbear/dropbear_ecdsa_host_key && -f /etc/dropbear/host_key ]] && dropbearconvert openssh dropbear /etc/dropbear/host_key /etc/dropbear/dropbear_ecdsa_host_key