--- qemu.conf	2018-03-21 18:30:47.000000000 +1100
+++ qemu.conf-fixed	2018-04-23 11:56:51.009533408 +1000
@@ -536,7 +536,7 @@
 # is used to create <source type='bridge'> interfaces when libvirtd is
 # running unprivileged.  libvirt invokes the helper directly, instead
 # of using "-netdev bridge", for security reasons.
-#bridge_helper = "/usr/libexec/qemu-bridge-helper"
+bridge_helper = "/usr/lib/qemu/qemu-bridge-helper"