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..91e24a9 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