diff --git a/db/post_migrate/20251215205262_finalize_user_agent_details_organization_id_backfill.rb b/db/post_migrate/20251215205262_finalize_user_agent_details_organization_id_backfill.rb
new file mode 100644
index 0000000000000000000000000000000000000000..660c4fc3e260294fd12e771c7c64b4bef2dbaf5e
--- /dev/null
+++ b/db/post_migrate/20251215205262_finalize_user_agent_details_organization_id_backfill.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class FinalizeUserAgentDetailsOrganizationIdBackfill < Gitlab::Database::Migration[2.3]
+  disable_ddl_transaction!
+  milestone '18.9'
+  restrict_gitlab_migration gitlab_schema: :gitlab_main_org
+
+  MIGRATION = 'BackfillUserAgentDetailsOrganizationId'
+
+  def up
+    ensure_batched_background_migration_is_finished(
+      job_class_name: MIGRATION,
+      table_name: :user_agent_details,
+      column_name: :id,
+      job_arguments: [],
+      finalize: true
+    )
+  end
+
+  def down
+    # no-op
+  end
+end
diff --git a/db/post_migrate/20251215205265_add_not_null_constraint_to_user_agent_details_on_organization_id.rb b/db/post_migrate/20251215205265_add_not_null_constraint_to_user_agent_details_on_organization_id.rb
new file mode 100644
index 0000000000000000000000000000000000000000..b87793dade4f615182812ce60b0cd78ac7b23f01
--- /dev/null
+++ b/db/post_migrate/20251215205265_add_not_null_constraint_to_user_agent_details_on_organization_id.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class AddNotNullConstraintToUserAgentDetailsOnOrganizationId < Gitlab::Database::Migration[2.3]
+  disable_ddl_transaction!
+  milestone '18.9'
+
+  def up
+    add_not_null_constraint :user_agent_details, :organization_id, validate: false
+  end
+
+  def down
+    remove_not_null_constraint :user_agent_details, :organization_id
+  end
+end
diff --git a/db/post_migrate/20251215205270_prepare_user_agent_details_organization_id_not_null_validation.rb b/db/post_migrate/20251215205270_prepare_user_agent_details_organization_id_not_null_validation.rb
new file mode 100644
index 0000000000000000000000000000000000000000..44b79d4dcc0e98ac5593aa9fe069b74aeb33c290
--- /dev/null
+++ b/db/post_migrate/20251215205270_prepare_user_agent_details_organization_id_not_null_validation.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class PrepareUserAgentDetailsOrganizationIdNotNullValidation < Gitlab::Database::Migration[2.3]
+  milestone '18.9'
+  CONSTRAINT_NAME = 'check_17a3a18e31'
+
+  def up
+    prepare_async_check_constraint_validation :user_agent_details, name: CONSTRAINT_NAME
+  end
+
+  def down
+    unprepare_async_check_constraint_validation :user_agent_details, name: CONSTRAINT_NAME
+  end
+end
diff --git a/db/schema_migrations/20251215205262 b/db/schema_migrations/20251215205262
new file mode 100644
index 0000000000000000000000000000000000000000..bcbc132ec067e5c369fae7bde42bb76df580a708
--- /dev/null
+++ b/db/schema_migrations/20251215205262
@@ -0,0 +1 @@
+c46c4671c35684946e97275a11ee645a7d0aa29ca00421430b83232e931d21a1
\ No newline at end of file
diff --git a/db/schema_migrations/20251215205265 b/db/schema_migrations/20251215205265
new file mode 100644
index 0000000000000000000000000000000000000000..19678bffe6d65548cfeea9fe85d6e9bf14fec797
--- /dev/null
+++ b/db/schema_migrations/20251215205265
@@ -0,0 +1 @@
+630bb6fd777f150d726835b50a5ba12882e5222646e9d0bcb817d301457811b8
\ No newline at end of file
diff --git a/db/schema_migrations/20251215205270 b/db/schema_migrations/20251215205270
new file mode 100644
index 0000000000000000000000000000000000000000..544e7d6700616418346da8da7b7033cbf637dde5
--- /dev/null
+++ b/db/schema_migrations/20251215205270
@@ -0,0 +1 @@
+36a103f7975527b41fb3d6b92a531d9f1caf5b2ccca75a61f1dff59fe132c711
\ No newline at end of file
diff --git a/db/structure.sql b/db/structure.sql
index df4c50822b7291d56b0616981711c011dad18d47..3dfd5fb64a48498055adabfad89b7707dabd77fb 100644
--- a/db/structure.sql
+++ b/db/structure.sql
@@ -35047,6 +35047,9 @@ ALTER TABLE epic_issues
 ALTER TABLE bulk_import_batch_trackers
     ADD CONSTRAINT check_13004cd9a8 CHECK ((num_nonnulls(namespace_id, organization_id, project_id) = 1)) NOT VALID;
 
+ALTER TABLE user_agent_details
+    ADD CONSTRAINT check_17a3a18e31 CHECK ((organization_id IS NOT NULL)) NOT VALID;
+
 ALTER TABLE workspaces
     ADD CONSTRAINT check_2a89035b04 CHECK ((personal_access_token_id IS NOT NULL)) NOT VALID;
 
diff --git a/spec/services/spam/akismet_mark_as_spam_service_spec.rb b/spec/services/spam/akismet_mark_as_spam_service_spec.rb
index aec80227829bac136443e1f4f56813ea0ba1f071..f07fa8d262b8358fff720d82f0939aac9b5f6cbd 100644
--- a/spec/services/spam/akismet_mark_as_spam_service_spec.rb
+++ b/spec/services/spam/akismet_mark_as_spam_service_spec.rb
@@ -40,12 +40,6 @@
         subject.execute
       end
 
-      context 'when an organization is not assigned to the record' do
-        let(:user_agent_detail) { build(:user_agent_detail, organization: nil) }
-
-        it { expect(subject.execute).to be_truthy }
-      end
-
       context 'when Akismet does not consider it spam' do
         it 'does not update the spammable object as spam' do
           allow(fake_akismet_service).to receive(:submit_spam).and_return false