diff --git a/install_postfix_advanced.sh b/install_postfix_advanced.sh
index 37d1cd0..71316d2 100755
--- a/install_postfix_advanced.sh
+++ b/install_postfix_advanced.sh
@@ -4147,6 +4147,14 @@ else
    dmarc_pipe_present=false
 fi
 
+if ${LISTEN_ON_ADDITIONAL_RELAY_PORT} ; then
+   if grep -iq -E "^${ADDITIONAL_RELAY_LISTEN_PORT}\s+" $postfix_master_cf > /dev/null 2>&1 ; then
+      additional_relay_port_present=true
+   else
+      additional_relay_port_present=false
+   fi
+fi
+
 _found=false
 echononl "   Create new file \"${postfix_master_cf}\""
 if [[ -f "${postfix_master_cf}.$backup_date" ]]; then
@@ -4176,9 +4184,11 @@ smtps     inet  n       -       y       -       -       smtpd
 EOF
 				fi
          elif $LISTEN_ON_ADDITIONAL_RELAY_PORT ; then
-            cat >> $postfix_master_cf << EOF
+            if ! ${additional_relay_port_present} ; then
+               cat >> $postfix_master_cf << EOF
 ${ADDITIONAL_RELAY_LISTEN_PORT}      inet  n       -       y       -       -       smtpd
 EOF
+            fi
 			fi
 			continue
 		fi