diff --git a/cloudformation/cfncluster.cfn.json b/cloudformation/cfncluster.cfn.json
index 425dd0c8c4..3466f7024f 100644
--- a/cloudformation/cfncluster.cfn.json
+++ b/cloudformation/cfncluster.cfn.json
@@ -7,8 +7,8 @@
       "Type" : "String",
       "MinLength" : "1",
       "MaxLength" : "64",
-      "AllowedPattern" : "[-_ a-zA-Z0-9]*",
-      "ConstraintDescription" : "can contain only alphanumeric characters, spaces, dashes and underscores."
+      "AllowedPattern" : "[-+_.@ a-zA-Z0-9]+",
+      "ConstraintDescription" : "can contain only alphanumeric characters, spaces, dashes, plusses, underscores, dots, and at signs."
     },
     "MasterInstanceType" : {
       "Description" : "Master Server EC2 instance type",