diff --git a/environment_config.yaml b/environment_config.yaml
index 298133fde..9ac4b90f2 100644
--- a/environment_config.yaml
+++ b/environment_config.yaml
@@ -29,7 +29,7 @@ attributes:
     weight: 50
     type: "text"
     regex:
-      source: '^(?!(?:0(?:\.0){3}|255(?:\.255){3})$)(?:\d|1?\d\d|2[0-4]\d|25[0-5])(?:\.(?:\d|1?\d\d|2[0-4]\d|25[0-5])){3}$'
+      source: '^(?!(?:0(?:\.0){3}|255(?:\.255){3})\/([1-9]|[1-2]\d|3[0-2])$)(?:\d|1?\d\d|2[0-4]\d|25[0-5])(?:\.(?:\d|1?\d\d|2[0-4]\d|25[0-5])){3}\/([1-9]|[1-2]\d|3[0-2])$'
       error: "Invalid CIDR"
   contrail_route_target:
     value: '10000'