diff --git a/lib/neutron b/lib/neutron
index b05b16d..3808165 100644
--- a/lib/neutron
+++ b/lib/neutron
@@ -744,6 +744,16 @@
 # Utility Functions
 #------------------
 
+# _neutron_service_plugin_class_add() - add service plugin class
+function _neutron_service_plugin_class_add() {
+    local service_plugin_class=$1
+    if [[ $Q_SERVICE_PLUGIN_CLASSES == '' ]]; then
+        Q_SERVICE_PLUGIN_CLASSES=$service_plugin_class
+    elif [[ ! ,${Q_SERVICE_PLUGIN_CLASSES}, =~ ,${service_plugin_class}, ]]; then
+        Q_SERVICE_PLUGIN_CLASSES="$Q_SERVICE_PLUGIN_CLASSES,$service_plugin_class"
+    fi
+}
+
 # _neutron_setup_rootwrap() - configure Neutron's rootwrap
 function _neutron_setup_rootwrap() {
     if [[ "$Q_USE_ROOTWRAP" == "False" ]]; then
diff --git a/lib/neutron_plugins/ml2 b/lib/neutron_plugins/ml2
index b5b1873..ab4e347 100644
--- a/lib/neutron_plugins/ml2
+++ b/lib/neutron_plugins/ml2
@@ -54,11 +54,7 @@
     Q_PLUGIN_CLASS="neutron.plugins.ml2.plugin.Ml2Plugin"
     # The ML2 plugin delegates L3 routing/NAT functionality to
     # the L3 service plugin which must therefore be specified.
-    if [[ $Q_SERVICE_PLUGIN_CLASSES == '' ]]; then
-        Q_SERVICE_PLUGIN_CLASSES=$ML2_L3_PLUGIN
-    else
-        Q_SERVICE_PLUGIN_CLASSES="$Q_SERVICE_PLUGIN_CLASSES,$ML2_L3_PLUGIN"
-    fi
+    _neutron_service_plugin_class_add $ML2_L3_PLUGIN
 }
 
 function neutron_plugin_configure_service() {
diff --git a/lib/neutron_plugins/services/firewall b/lib/neutron_plugins/services/firewall
index 1597e85..97cc5a2 100644
--- a/lib/neutron_plugins/services/firewall
+++ b/lib/neutron_plugins/services/firewall
@@ -8,11 +8,7 @@
 FWAAS_PLUGIN=neutron.services.firewall.fwaas_plugin.FirewallPlugin
 
 function neutron_fwaas_configure_common() {
-    if [[ $Q_SERVICE_PLUGIN_CLASSES == '' ]]; then
-        Q_SERVICE_PLUGIN_CLASSES=$FWAAS_PLUGIN
-    else
-        Q_SERVICE_PLUGIN_CLASSES="$Q_SERVICE_PLUGIN_CLASSES,$FWAAS_PLUGIN"
-    fi
+    _neutron_service_plugin_class_add $FWAAS_PLUGIN
 }
 
 function neutron_fwaas_configure_driver() {
diff --git a/lib/neutron_plugins/services/loadbalancer b/lib/neutron_plugins/services/loadbalancer
index c38f904..6ff991c 100644
--- a/lib/neutron_plugins/services/loadbalancer
+++ b/lib/neutron_plugins/services/loadbalancer
@@ -19,11 +19,7 @@
 }
 
 function neutron_agent_lbaas_configure_common() {
-    if [[ $Q_SERVICE_PLUGIN_CLASSES == '' ]]; then
-        Q_SERVICE_PLUGIN_CLASSES=$LBAAS_PLUGIN
-    else
-        Q_SERVICE_PLUGIN_CLASSES="$Q_SERVICE_PLUGIN_CLASSES,$LBAAS_PLUGIN"
-    fi
+    _neutron_service_plugin_class_add $LBAAS_PLUGIN
 }
 
 function neutron_agent_lbaas_configure_agent() {
diff --git a/lib/neutron_plugins/services/metering b/lib/neutron_plugins/services/metering
index 629f3b7..5cabfbf 100644
--- a/lib/neutron_plugins/services/metering
+++ b/lib/neutron_plugins/services/metering
@@ -10,11 +10,7 @@
 METERING_PLUGIN="neutron.services.metering.metering_plugin.MeteringPlugin"
 
 function neutron_agent_metering_configure_common() {
-    if [[ $Q_SERVICE_PLUGIN_CLASSES == '' ]]; then
-        Q_SERVICE_PLUGIN_CLASSES=$METERING_PLUGIN
-    else
-        Q_SERVICE_PLUGIN_CLASSES="$Q_SERVICE_PLUGIN_CLASSES,$METERING_PLUGIN"
-    fi
+    _neutron_service_plugin_class_add $METERING_PLUGIN
 }
 
 function neutron_agent_metering_configure_agent() {
diff --git a/lib/neutron_plugins/services/vpn b/lib/neutron_plugins/services/vpn
index b8f5c7d..1ab07cb 100644
--- a/lib/neutron_plugins/services/vpn
+++ b/lib/neutron_plugins/services/vpn
@@ -15,11 +15,7 @@
 }
 
 function neutron_vpn_configure_common() {
-    if [[ $Q_SERVICE_PLUGIN_CLASSES == '' ]]; then
-        Q_SERVICE_PLUGIN_CLASSES=$VPN_PLUGIN
-    else
-        Q_SERVICE_PLUGIN_CLASSES="$Q_SERVICE_PLUGIN_CLASSES,$VPN_PLUGIN"
-    fi
+    _neutron_service_plugin_class_add $VPN_PLUGIN
 }
 
 # Restore xtrace