diff --git a/dom0-updates/qubes-dom0-update b/dom0-updates/qubes-dom0-update
index e23455e..3eb5d4e 100755
--- a/dom0-updates/qubes-dom0-update
+++ b/dom0-updates/qubes-dom0-update
@@ -41,6 +41,13 @@ if [ "$1" = "--help" ]; then
     exit
 fi
 
+exec 9>"/var/lock/qubes-dom0-update.lock"
+flock -n 9
+if [[ ${?} -ne 0 ]]; then
+    echo "Another instance of qubes-dom0-update is already running!"
+    exit 1
+fi
+
 PKGS=()
 YUM_OPTS=()
 UPDATEVM_OPTS=()