diff --git a/db/post_migrate/20250723001901_add_design_management_designs_versions_namespace_id_not_null_constraint.rb b/db/post_migrate/20250723001901_add_design_management_designs_versions_namespace_id_not_null_constraint.rb
new file mode 100644
index 0000000000000000000000000000000000000000..f8d7ed63d8aec1fab9d54be34b98ab26b887022a
--- /dev/null
+++ b/db/post_migrate/20250723001901_add_design_management_designs_versions_namespace_id_not_null_constraint.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+# See https://docs.gitlab.com/ee/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddDesignManagementDesignsVersionsNamespaceIdNotNullConstraint < Gitlab::Database::Migration[2.3]
+  disable_ddl_transaction!
+  milestone '18.3'
+
+  def up
+    add_not_null_constraint :design_management_designs_versions, :namespace_id
+  end
+
+  def down
+    remove_not_null_constraint :design_management_designs_versions, :namespace_id
+  end
+end
diff --git a/db/schema_migrations/20250723001901 b/db/schema_migrations/20250723001901
new file mode 100644
index 0000000000000000000000000000000000000000..f07d108ebad9d7611d1000bd662b79bf410eb9ba
--- /dev/null
+++ b/db/schema_migrations/20250723001901
@@ -0,0 +1 @@
+c6ec3b7fa54ff8702260679cbf81ee1e694399ebb917033f69fb5a6bd08d1658
\ No newline at end of file