diff --git a/modules/organization/README.md b/modules/organization/README.md
index 993c5dcdf..16c7fc4c6 100644
--- a/modules/organization/README.md
+++ b/modules/organization/README.md
@@ -64,7 +64,7 @@ module "org" {
 
 | name | description | type | required | default |
 |---|---|:---: |:---:|:---:|
-| org_id | Organization id in nnnnnn format. | <code title="">number</code> | ✓ |  |
+| organization_id | Organization id in organizations/nnnnnn format. | <code title="string&#10;validation &#123;&#10;condition     &#61; can&#40;regex&#40;&#34;&#94;organizations&#47;&#91;0-9&#93;&#43;&#34;, var.organization_id&#41;&#41;&#10;error_message &#61; &#34;The organization_id must in the form organizations&#47;nnn.&#34;&#10;&#125;">string</code> | ✓ |  |
 | *custom_roles* | Map of role name => list of permissions to create in this project. | <code title="map&#40;list&#40;string&#41;&#41;">map(list(string))</code> |  | <code title="">{}</code> |
 | *firewall_policies* | Hierarchical firewall policies to *create* in the organization. | <code title="map&#40;map&#40;object&#40;&#123;&#10;description             &#61; string&#10;direction               &#61; string&#10;action                  &#61; string&#10;priority                &#61; number&#10;ranges                  &#61; list&#40;string&#41;&#10;ports                   &#61; map&#40;list&#40;string&#41;&#41;&#10;target_service_accounts &#61; list&#40;string&#41;&#10;target_resources        &#61; list&#40;string&#41;&#10;logging                 &#61; bool&#10;&#125;&#41;&#41;&#41;">map(map(object({...})))</code> |  | <code title="">{}</code> |
 | *firewall_policy_attachments* | List of hierarchical firewall policy IDs to *attach* to the organization | <code title="map&#40;string&#41;">map(string)</code> |  | <code title="">{}</code> |
@@ -81,5 +81,5 @@ module "org" {
 |---|---|:---:|
 | firewall_policies | Map of firewall policy resources created in the organization. |  |
 | firewall_policy_id | Map of firewall policy ids created in the organization. |  |
-| org_id | Organization id dependent on module resources. |  |
+| organization_id | Organization id dependent on module resources. |  |
 <!-- END TFDOC -->
diff --git a/modules/organization/main.tf b/modules/organization/main.tf
index d87fcab5f..f3b751664 100644
--- a/modules/organization/main.tf
+++ b/modules/organization/main.tf
@@ -15,6 +15,7 @@
  */
 
 locals {
+  organization_id_numeric = split("/", var.organization_id)[1]
   iam_additive_pairs = flatten([
     for role, members in var.iam_additive : [
       for member in members : { role = role, member = member }
@@ -43,7 +44,7 @@ locals {
 
 resource "google_organization_iam_custom_role" "roles" {
   for_each    = var.custom_roles
-  org_id      = var.org_id
+  org_id      = local.organization_id_numeric
   role_id     = each.key
   title       = "Custom role ${each.key}"
   description = "Terraform-managed"
@@ -52,7 +53,7 @@ resource "google_organization_iam_custom_role" "roles" {
 
 resource "google_organization_iam_binding" "authoritative" {
   for_each = var.iam
-  org_id   = var.org_id
+  org_id   = local.organization_id_numeric
   role     = each.key
   members  = each.value
 }
@@ -63,14 +64,14 @@ resource "google_organization_iam_member" "additive" {
     ? local.iam_additive
     : {}
   )
-  org_id = var.org_id
+  org_id = local.organization_id_numeric
   role   = each.value.role
   member = each.value.member
 }
 
 resource "google_organization_iam_audit_config" "config" {
   for_each = var.iam_audit_config
-  org_id   = var.org_id
+  org_id   = local.organization_id_numeric
   service  = each.key
   dynamic audit_log_config {
     for_each = each.value
@@ -84,7 +85,7 @@ resource "google_organization_iam_audit_config" "config" {
 
 resource "google_organization_policy" "boolean" {
   for_each   = var.policy_boolean
-  org_id     = var.org_id
+  org_id     = local.organization_id_numeric
   constraint = each.key
 
   dynamic boolean_policy {
@@ -105,7 +106,7 @@ resource "google_organization_policy" "boolean" {
 
 resource "google_organization_policy" "list" {
   for_each   = var.policy_list
-  org_id     = var.org_id
+  org_id     = local.organization_id_numeric
   constraint = each.key
 
   dynamic list_policy {
@@ -160,7 +161,7 @@ resource "google_compute_organization_security_policy" "policy" {
   for_each = var.firewall_policies
 
   display_name = each.key
-  parent       = "organizations/${var.org_id}"
+  parent       = var.organization_id
 }
 
 resource "google_compute_organization_security_policy_rule" "rule" {
@@ -195,7 +196,7 @@ resource "google_compute_organization_security_policy_rule" "rule" {
 resource "google_compute_organization_security_policy_association" "attachment" {
   provider      = google-beta
   for_each      = var.firewall_policy_attachments
-  name          = "organizations/${var.org_id}-${each.key}"
-  attachment_id = "organizations/${var.org_id}"
+  name          = "${var.organization_id}-${each.key}"
+  attachment_id = var.organization_id
   policy_id     = each.value
 }
diff --git a/modules/organization/outputs.tf b/modules/organization/outputs.tf
index f6e52441a..dd0d0294e 100644
--- a/modules/organization/outputs.tf
+++ b/modules/organization/outputs.tf
@@ -14,9 +14,9 @@
  * limitations under the License.
  */
 
-output "org_id" {
+output "organization_id" {
   description = "Organization id dependent on module resources."
-  value       = var.org_id
+  value       = var.organization_id
   depends_on = [
     google_organization_iam_audit_config.config,
     google_organization_iam_binding.authoritative,
diff --git a/modules/organization/variables.tf b/modules/organization/variables.tf
index 1fe3f1bdd..ea7b5f52e 100644
--- a/modules/organization/variables.tf
+++ b/modules/organization/variables.tf
@@ -49,9 +49,13 @@ variable "iam_audit_config" {
   # }
 }
 
-variable "org_id" {
-  description = "Organization id in nnnnnn format."
-  type        = number
+variable "organization_id" {
+  description = "Organization id in organizations/nnnnnn format."
+  type        = string
+  validation {
+    condition     = can(regex("^organizations/[0-9]+", var.organization_id))
+    error_message = "The organization_id must in the form organizations/nnn."
+  }
 }
 
 variable "policy_boolean" {
diff --git a/tests/modules/organization/fixture/main.tf b/tests/modules/organization/fixture/main.tf
index 90abee757..28bbe270f 100644
--- a/tests/modules/organization/fixture/main.tf
+++ b/tests/modules/organization/fixture/main.tf
@@ -16,7 +16,7 @@
 
 module "test" {
   source                      = "../../../../modules/organization"
-  org_id                      = 1234567890
+  organization_id             = "organizations/1234567890"
   custom_roles                = var.custom_roles
   iam                         = var.iam
   iam_additive                = var.iam_additive