@@ -90,7 +90,7 @@ source ./stackrc

 DEST=${DEST:-/opt/stack}

 # Check to see if we are already running a stack.sh

-if screen -ls | egrep -q "[0-9].stack"; then

+if type -p screen >/dev/null && screen -ls | egrep -q "[0-9].stack"; then

     echo "You are already running a stack.sh session."

     echo "To rejoin this session type 'screen -x stack'."

     echo "To destroy this session, kill the running screen."