diff --git a/lib/unitsml/unitsdb/database.rb b/lib/unitsml/unitsdb/database.rb
index 7a5be53..e0ff20b 100644
--- a/lib/unitsml/unitsdb/database.rb
+++ b/lib/unitsml/unitsdb/database.rb
@@ -3,18 +3,29 @@
 module Unitsml
   module Unitsdb
     class Database < ::Unitsdb::Database
-      DATABASE = nil
+      def self.load_opal_payload(payload)
+        @opal_payload = payload
+      end
 
       def self.from_db(dir_path, context: Unitsml::Configuration.context.id)
         return super unless RUBY_ENGINE == "opal"
 
         context_id = context.to_sym
-        raise Unitsml::Errors::OpalPayloadNotBundledError unless DATABASE
+        raise Unitsml::Errors::OpalPayloadNotBundledError unless opal_payload
 
+        # Ensure the UnitsML context is registered when context: is direct.
         Unitsml::Configuration.context
 
-        from_hash(DATABASE, register: context_id)
+        from_hash(opal_payload, register: context_id)
+      end
+
+      def self.opal_payload
+        return @opal_payload if instance_variable_defined?(:@opal_payload)
+        return unless const_defined?(:DATABASE, false)
+
+        @opal_payload = const_get(:DATABASE, false)
       end
+      private_class_method :opal_payload
 
       Configuration.register_model(self, id: :database)
     end
diff --git a/spec/unitsml/unitsdb/database_spec.rb b/spec/unitsml/unitsdb/database_spec.rb
index cfe495f..10b7036 100644
--- a/spec/unitsml/unitsdb/database_spec.rb
+++ b/spec/unitsml/unitsdb/database_spec.rb
@@ -21,7 +21,29 @@
     end
 
     context "when running on opal" do
-      before { stub_const("RUBY_ENGINE", "opal") }
+      def clear_opal_payload
+        return unless described_class.instance_variable_defined?(:@opal_payload)
+
+        described_class.remove_instance_variable(:@opal_payload)
+      end
+
+      before do
+        stub_const("RUBY_ENGINE", "opal")
+        clear_opal_payload
+      end
+
+      after do
+        clear_opal_payload
+      end
+
+      def allow_from_hash(database_class)
+        allow(database_class).to receive(:from_hash).and_return(:database)
+      end
+
+      def expect_loaded_payload(database_class, payload)
+        expect(database_class).to have_received(:from_hash)
+          .with(payload, register: :unitsml_ruby)
+      end
 
       it "raises a clear error when the bundled payload is missing" do
         expect do
@@ -29,6 +51,27 @@
         end.to raise_error(Unitsml::Errors::OpalPayloadNotBundledError,
                            /not bundled/)
       end
+
+      it "loads the bundled Opal payload" do
+        payload = { "units" => [] }
+        described_class.load_opal_payload(payload)
+        allow_from_hash(described_class)
+
+        expect(described_class.from_db("/does/not/matter",
+                                       context: :unitsml_ruby)).to eq(:database)
+        expect_loaded_payload(described_class, payload)
+      end
+
+      it "falls back to a legacy DATABASE constant" do
+        payload = { "units" => [:from_const] }
+        subclass = Class.new(described_class)
+        subclass.const_set(:DATABASE, payload)
+        allow_from_hash(subclass)
+
+        expect(subclass.from_db("/does/not/matter",
+                                context: :unitsml_ruby)).to eq(:database)
+        expect_loaded_payload(subclass, payload)
+      end
     end
   end
 
@@ -58,6 +101,49 @@
       end
     end
 
+    context "when running on opal with a loaded payload" do
+      let(:payload) { { "units" => [] } }
+
+      before do
+        stub_const("RUBY_ENGINE", "opal")
+        allow(Unitsml::Configuration).to receive(:context).and_call_original
+        clear_unitsdb_database_cache
+        clear_unitsml_database_cache
+        Unitsml::Configuration.context(force_populate: true)
+        Unitsml::Unitsdb::Database.load_opal_payload(payload)
+        allow(Unitsml::Unitsdb::Database)
+          .to receive(:from_hash)
+          .and_return(:opal_database)
+      end
+
+      after do
+        clear_unitsdb_database_cache
+        clear_unitsml_database_cache
+        clear_opal_payload
+      end
+
+      def clear_unitsdb_database_cache
+        Unitsdb.instance_variable_set(:@databases, nil)
+      end
+
+      def clear_unitsml_database_cache
+        described_class.instance_variable_set(:@database, nil)
+      end
+
+      def clear_opal_payload
+        database_class = Unitsml::Unitsdb::Database
+        return unless database_class.instance_variable_defined?(:@opal_payload)
+
+        database_class.remove_instance_variable(:@opal_payload)
+      end
+
+      it "loads the UnitsML database through the real unitsdb-ruby loader" do
+        expect(described_class.database).to eq(:opal_database)
+        expect(Unitsml::Unitsdb::Database).to have_received(:from_hash)
+          .with(payload, register: :unitsml_ruby)
+      end
+    end
+
     context "when unitsdb-ruby exposes a database loader" do
       before do
         stub_const("RUBY_ENGINE", "ruby")
diff --git a/spec/unitsml_spec.rb b/spec/unitsml_spec.rb
index 054263e..bc99558 100644
--- a/spec/unitsml_spec.rb
+++ b/spec/unitsml_spec.rb
@@ -1,10 +1,36 @@
 # frozen_string_literal: true
 
+require "open3"
+require "rbconfig"
+
 RSpec.describe Unitsml do
   it "has a version number" do
     expect(Unitsml::VERSION).not_to be_nil
   end
 
+  it "does not change an existing global XML adapter when required" do
+    lib_path = File.expand_path("../lib", __dir__)
+    script = <<~RUBY
+      require "lutaml/model"
+      Lutaml::Model::Config.xml_adapter_type = :nokogiri
+      require "unitsml"
+
+      unless Lutaml::Model::Config.xml_adapter_type == :nokogiri
+        abort "expected :nokogiri, got \#{Lutaml::Model::Config.xml_adapter_type.inspect}"
+      end
+    RUBY
+
+    _stdout, stderr, status = Open3.capture3(
+      RbConfig.ruby,
+      "-I",
+      lib_path,
+      "-e",
+      script,
+    )
+
+    expect(status).to be_success, stderr
+  end
+
   it "parses a basic unit expression" do
     formula = described_class.parse("mm")
     expect(formula).to be_a(Unitsml::Formula)