diff --git a/dockerfile-kasm-realvnc-vncviewer b/dockerfile-kasm-realvnc-vncviewer
index 94ae657..6a32009 100644
--- a/dockerfile-kasm-realvnc-vncviewer
+++ b/dockerfile-kasm-realvnc-vncviewer
@@ -1,5 +1,6 @@
 ARG BASE_TAG="develop"
-FROM kasmweb/core-ubuntu-bionic:$BASE_TAG
+ARG BASE_IMAGE="core-ubuntu-focal"
+FROM kasmweb/$BASE_IMAGE:$BASE_TAG
 USER root
 
 ENV HOME /home/kasm-default-profile
diff --git a/src/ubuntu/install/realvnc_vncviewer/custom_startup.sh b/src/ubuntu/install/realvnc_vncviewer/custom_startup.sh
index c88bba1..6e75912 100644
--- a/src/ubuntu/install/realvnc_vncviewer/custom_startup.sh
+++ b/src/ubuntu/install/realvnc_vncviewer/custom_startup.sh
@@ -2,7 +2,8 @@
 set -ex
 START_COMMAND="/usr/bin/vncviewer"
 PGREP="vncviewer"
-MAXIMUS="false"
+export MAXIMIZE="false"
+MAXIMIZE_SCRIPT=$STARTUPDIR/maximize_window.sh
 DEFAULT_ARGS=""
 ARGS=${APP_ARGS:-$DEFAULT_ARGS}
 
@@ -38,6 +39,7 @@ kasm_exec() {
     if [ -n "$URL" ] ; then
         /usr/bin/filter_ready
         /usr/bin/desktop_ready
+        bash ${MAXIMIZE_SCRIPT} &
         $START_COMMAND $ARGS $OPT_URL
     else
         echo "No URL specified for exec command. Doing nothing."
@@ -53,10 +55,6 @@ kasm_startup() {
 
     if [ -z "$DISABLE_CUSTOM_STARTUP" ] ||  [ -n "$FORCE" ] ; then
 
-        if [[ $MAXIMUS == 'true' ]] ; then
-            maximus &
-        fi
-
         while true
         do
             if ! pgrep -x $PGREP > /dev/null
@@ -64,6 +62,7 @@ kasm_startup() {
                 /usr/bin/filter_ready
                 /usr/bin/desktop_ready
                 set +e
+                bash ${MAXIMIZE_SCRIPT} &
                 $START_COMMAND $ARGS $URL
                 set -e
             fi