diff --git a/doc/source/advanced_deployment/network_isolation.rst b/doc/source/advanced_deployment/network_isolation.rst
index 33b9a234..94f0fbd6 100644
--- a/doc/source/advanced_deployment/network_isolation.rst
+++ b/doc/source/advanced_deployment/network_isolation.rst
@@ -792,7 +792,7 @@ the environment)::
 
   parameter_defaults:
     # CIDR subnet mask length for provisioning network
-    ControlPlaneSubnetCidr: 24
+    ControlPlaneSubnetCidr: '24'
     # Gateway router for the provisioning network (or Undercloud IP)
     ControlPlaneDefaultRoute:10.8.146.254
     # Generally the IP of the Undercloud