diff --git a/lib/active_outbox/outboxable.rb b/lib/active_outbox/outboxable.rb
index e1840d1..edeed26 100644
--- a/lib/active_outbox/outboxable.rb
+++ b/lib/active_outbox/outboxable.rb
@@ -74,11 +74,11 @@ def outbox_model_name_from_config
 
     def namespace_outbox_mapping
       namespace = self.class.name.split('/').first
-
       ActiveOutbox.configuration.outbox_mapping[namespace&.underscore]
     end
 
     def default_outbox_mapping
+      # byebug
       ActiveOutbox.configuration.outbox_mapping['default']
     end
 
diff --git a/spec/lib/active_outbox/outboxable_spec.rb b/spec/lib/active_outbox/outboxable_spec.rb
index 603c0a2..ea0eb54 100644
--- a/spec/lib/active_outbox/outboxable_spec.rb
+++ b/spec/lib/active_outbox/outboxable_spec.rb
@@ -108,6 +108,18 @@
         include_examples 'raises an error and does not create neither the record nor the outbox record',
                          ActiveRecord::RecordNotSaved
       end
+
+      context 'when the ActiveOutbox configuration is not set' do
+        before do
+          # active_outbox = instance_double(ActiveOutbox)
+          # allow(ActiveOutbox).to receive(:new).and_return(active_outbox)
+          allow(ActiveOutbox.configuration).to receive(:outbox_mapping).and_return({ 'default' => nil })
+        end
+
+        it 'raises an error' do
+          expect { save_instance }.to raise_error(ActiveOutbox::OutboxClassNotFoundError)
+        end
+      end
     end
 
     context 'when the record could not be created' do
diff --git a/spec/support/00_outbox_config.rb b/spec/support/00_outbox_config.rb
index 142a043..de1cf4e 100644
--- a/spec/support/00_outbox_config.rb
+++ b/spec/support/00_outbox_config.rb
@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 ActiveOutbox.configure do |config|
+  # byebug
   config.outbox_mapping.merge!(
     'default' => 'Outbox'
   )