diff --git a/dockerfiles/start.sh b/dockerfiles/start.sh
index 780ec835..1082919c 100755
--- a/dockerfiles/start.sh
+++ b/dockerfiles/start.sh
@@ -45,8 +45,11 @@ ln -s $INSTALL_DIR/pialert/front /var/www/html/pialert
 sudo rm /etc/nginx/conf.d/pialert.conf
 # create symbolic link to NGINX configuaration coming with PiAlert
 sudo ln -s "$INSTALL_DIR/pialert/install/pialert.conf" /etc/nginx/conf.d/pialert.conf
-# use user-supplied port
-sudo sed -i 's/listen 80/listen '"$PORT"'/g' /etc/nginx/conf.d/pialert.conf
+
+# Use user-supplied port if set
+if [ -n "${PORT}" ]; then  
+  sudo sed -i 's/listen 20211/listen '"$PORT"'/g' /etc/nginx/conf.d/pialert.conf
+fi
 
 # Change web interface address if set
 if [ -n "${LISTEN_ADDR}" ]; then  
diff --git a/install/pialert.conf b/install/pialert.conf
index 387791c2..8821dee3 100755
--- a/install/pialert.conf
+++ b/install/pialert.conf
@@ -1,5 +1,5 @@
 server {
-    listen 80 default_server;
+    listen 20211 default_server;
     root /var/www/html;
     index index.php;
     #rewrite /pialert/(.*) / permanent;
@@ -15,4 +15,4 @@ server {
           fastcgi_send_timeout 600;
           fastcgi_read_timeout 600;
   }
-}
\ No newline at end of file
+}