diff --git a/.rubocop_todo/rspec/feature_category.yml b/.rubocop_todo/rspec/feature_category.yml
index 024b0d8c8580285dab9b8bf33c4c9280ec430f59..217ef323ee3d2bd3ca7802570f9723725c2fa358 100644
--- a/.rubocop_todo/rspec/feature_category.yml
+++ b/.rubocop_todo/rspec/feature_category.yml
@@ -3198,7 +3198,6 @@ RSpec/FeatureCategory:
     - 'spec/models/event_collection_spec.rb'
     - 'spec/models/external_issue_spec.rb'
     - 'spec/models/fork_network_member_spec.rb'
-    - 'spec/models/fork_network_spec.rb'
     - 'spec/models/generic_commit_status_spec.rb'
     - 'spec/models/gpg_key_spec.rb'
     - 'spec/models/gpg_key_subkey_spec.rb'
diff --git a/app/models/fork_network.rb b/app/models/fork_network.rb
index d40cba138ba235296bec52c1ccecfab5950abaf2..70d5bb25774cabcfaebe8b7f473c1bd4a330308a 100644
--- a/app/models/fork_network.rb
+++ b/app/models/fork_network.rb
@@ -2,7 +2,7 @@
 
 class ForkNetwork < ApplicationRecord
   belongs_to :root_project, class_name: 'Project'
-  belongs_to :organization, class_name: 'Organizations::Organization', optional: true
+  belongs_to :organization, class_name: 'Organizations::Organization'
 
   has_many :fork_network_members
   has_many :projects, through: :fork_network_members
diff --git a/db/migrate/20250415124320_add_not_null_to_fork_networks_organization_id.rb b/db/migrate/20250415124320_add_not_null_to_fork_networks_organization_id.rb
new file mode 100644
index 0000000000000000000000000000000000000000..d8138ad66fadcd8b939b8f6a36ecaf77ef856c71
--- /dev/null
+++ b/db/migrate/20250415124320_add_not_null_to_fork_networks_organization_id.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+class AddNotNullToForkNetworksOrganizationId < Gitlab::Database::Migration[2.2]
+  disable_ddl_transaction!
+
+  milestone '18.0'
+
+  def up
+    change_column_null :fork_networks, :organization_id, false
+  end
+
+  def down
+    change_column_null :fork_networks, :organization_id, true
+  end
+end
diff --git a/db/schema_migrations/20250415124320 b/db/schema_migrations/20250415124320
new file mode 100644
index 0000000000000000000000000000000000000000..f08f67131abe611058c56d9b0e2608fe6a0cbc95
--- /dev/null
+++ b/db/schema_migrations/20250415124320
@@ -0,0 +1 @@
+9f7be8572dc499518d406e34e9c288c8b0814ffa7e64eb6f4b2ebf00ce2e2f81
\ No newline at end of file
diff --git a/db/structure.sql b/db/structure.sql
index 9569d7557e80c4110b0c8a61b87f1f2367c8c6b2..9393178588105e26e742dd4363360b0af95ce731 100644
--- a/db/structure.sql
+++ b/db/structure.sql
@@ -14588,7 +14588,7 @@ CREATE TABLE fork_networks (
     id bigint NOT NULL,
     root_project_id bigint,
     deleted_root_project_name character varying,
-    organization_id bigint
+    organization_id bigint NOT NULL
 );
 
 CREATE SEQUENCE fork_networks_id_seq
diff --git a/spec/lib/gitlab/background_migration/backfill_organization_id_on_fork_networks_spec.rb b/spec/lib/gitlab/background_migration/backfill_organization_id_on_fork_networks_spec.rb
index 6391413324f671c3ebc614203ac6cee004c839d8..7581588377c7726847d879c118124235f416301e 100644
--- a/spec/lib/gitlab/background_migration/backfill_organization_id_on_fork_networks_spec.rb
+++ b/spec/lib/gitlab/background_migration/backfill_organization_id_on_fork_networks_spec.rb
@@ -41,8 +41,24 @@
     }
   end
 
+  let(:connection) { ActiveRecord::Base.connection }
+
   subject(:perform_migration) { described_class.new(**args).perform }
 
+  around do |example|
+    connection.transaction do
+      connection.execute(<<~SQL)
+        ALTER TABLE fork_networks ALTER COLUMN organization_id DROP NOT NULL;
+      SQL
+
+      example.run
+
+      connection.execute(<<~SQL)
+        ALTER TABLE fork_networks ALTER COLUMN organization_id SET NOT NULL;
+      SQL
+    end
+  end
+
   context 'when root project exists' do
     let(:fork_network) { fork_networks_table.create!(root_project_id: project.id) }
 
diff --git a/spec/models/fork_network_spec.rb b/spec/models/fork_network_spec.rb
index f2ec0ccb4fd93c13afe76975e329640dcf87aa8c..6b7484262cb43e89e2b5d77a627797b097dedd2a 100644
--- a/spec/models/fork_network_spec.rb
+++ b/spec/models/fork_network_spec.rb
@@ -2,13 +2,17 @@
 
 require 'spec_helper'
 
-RSpec.describe ForkNetwork do
+RSpec.describe ForkNetwork, feature_category: :source_code_management do
   include ProjectForksHelper
 
+  describe "validations" do
+    it { is_expected.to belong_to(:organization) }
+  end
+
   describe '#add_root_as_member' do
     it 'adds the root project as a member when creating a new root network' do
       project = create(:project)
-      fork_network = described_class.create!(root_project: project)
+      fork_network = described_class.create!(root_project: project, organization_id: project.organization_id)
 
       expect(fork_network.projects).to include(project)
     end