diff --git a/templates/workspace_services/guacamole/user_resources/guacamole-azure-linuxvm/terraform/locals.tf b/templates/workspace_services/guacamole/user_resources/guacamole-azure-linuxvm/terraform/locals.tf
index cc25f06ab..fd2266eee 100644
--- a/templates/workspace_services/guacamole/user_resources/guacamole-azure-linuxvm/terraform/locals.tf
+++ b/templates/workspace_services/guacamole/user_resources/guacamole-azure-linuxvm/terraform/locals.tf
@@ -8,7 +8,7 @@ locals {
   keyvault_name                  = lower("kv-${substr(local.workspace_resource_name_suffix, -20, -1)}")
   storage_name                   = lower(replace("stg${substr(local.workspace_resource_name_suffix, -8, -1)}", "-", ""))
   admin_username = (
-    length(data.azuread_user.user.mail) > 0 ?
+    ((length(data.azuread_user.user.mail) > 0) && (contains(data.azuread_user.user.user_principal_name, "#EXT#"))) ?
     substr(element(split("@", data.azuread_user.user.mail), 0), 0, 20) :
     substr(
       contains(element(split("@", data.azuread_user.user.user_principal_name), 0), "#EXT#") ?
diff --git a/templates/workspace_services/guacamole/user_resources/guacamole-azure-windowsvm/terraform/locals.tf b/templates/workspace_services/guacamole/user_resources/guacamole-azure-windowsvm/terraform/locals.tf
index 62e921ab7..ca8a63258 100644
--- a/templates/workspace_services/guacamole/user_resources/guacamole-azure-windowsvm/terraform/locals.tf
+++ b/templates/workspace_services/guacamole/user_resources/guacamole-azure-windowsvm/terraform/locals.tf
@@ -8,7 +8,7 @@ locals {
   keyvault_name                  = lower("kv-${substr(local.workspace_resource_name_suffix, -20, -1)}")
   storage_name                   = lower(replace("stg${substr(local.workspace_resource_name_suffix, -8, -1)}", "-", ""))
   admin_username = (
-    length(data.azuread_user.user.mail) > 0 ?
+    ((length(data.azuread_user.user.mail) > 0) && (contains(data.azuread_user.user.user_principal_name, "#EXT#"))) ?
     substr(element(split("@", data.azuread_user.user.mail), 0), 0, 20) :
     substr(
       contains(element(split("@", data.azuread_user.user.user_principal_name), 0), "#EXT#") ?