diff --git a/plugin.sh b/plugin.sh
index b17b43f..6cfcabc 100755
--- a/plugin.sh
+++ b/plugin.sh
@@ -64,7 +64,7 @@ output_versions(){
 run_stack_deploy() {
   echo "--- start deploy ---"
 
-  if [[ -z "${PLUGIN_REG_USER}" ]] && [[ -z "${PLUGIN_REG_PASS}" ]]; then
+  if [[ ! -z "${PLUGIN_REG_USER}" ]] && [[ ! -z "${PLUGIN_REG_PASS}" ]]; then
     echo "--- discovered secrets, assuming private registry, logging in ---"
     docker login -u "${PLUGIN_REG_USER}" -p "${PLUGIN_REG_PASS}"
     docker -H "$REMOTE_DOCKER_HOST" stack deploy -c "$PLUGIN_COMPOSE" "$PLUGIN_STACK"