diff --git a/entrypoint.sh b/entrypoint.sh
index 57dc81c..8523655 100755
--- a/entrypoint.sh
+++ b/entrypoint.sh
@@ -24,7 +24,7 @@ NGINX_CONF_FILE="/etc/nginx/conf.d/default.conf"
 INDEX_HTML_FILE="/usr/share/nginx/html/index.html";
 
 # Change default NGINX listen port if NGINX_HTTP_PORT env is set
-if [[ -v "${NGINX_HTTP_PORT}" ]]; then
+if [ ! -z "${NGINX_HTTP_PORT}" ]; then
   sed -i "s~listen 80~listen $NGINX_HTTP_PORT~g" $NGINX_CONF_FILE
   sed -i "s~listen \[\:\:\]\:80~listen [::]:$NGINX_HTTP_PORT~g" $NGINX_CONF_FILE
 fi