diff --git a/DEBIAN/postinst b/DEBIAN/postinst
index a0e7334..2311b35 100644
--- a/DEBIAN/postinst
+++ b/DEBIAN/postinst
@@ -37,9 +37,10 @@ EOF
 
 systemctl daemon-reload
 
-echo "> Writing default config parameters ..."
-touch $CONFIG_DIR/env
-cat <<EOF >$CONFIG_DIR/env
+if [[ ! -f $CONFIG_DIR/env ]]; then
+  echo "> Writing initial config ..."
+  touch $CONFIG_DIR/env
+  cat <<EOF >$CONFIG_DIR/env
 DLS_URL=127.0.0.1
 DLS_PORT=443
 LEASE_EXPIRE_DAYS=90
@@ -48,6 +49,7 @@ INSTANCE_KEY_RSA=$CONFIG_DIR/instance.private.pem
 INSTANCE_KEY_PUB=$CONFIG_DIR/instance.public.pem
 
 EOF
+fi
 
 echo "> Create dls-instance keypair ..."
 openssl genrsa -out $CONFIG_DIR/instance.private.pem 2048
@@ -72,7 +74,8 @@ if [[ -f $CONFIG_DIR/webserver.key ]]; then
 
   if [ -x "$(command -v curl)" ]; then
     echo "> Testing API ..."
-    curl --insecure -X GET https://127.0.0.1/status
+    source $CONFIG_DIR/env
+    curl --insecure -X GET https://$DLS_URL:$DLS_PORT/status
   else
     echo "> Testing API failed, curl not available. Please test manually!"
   fi