diff --git a/lib/api.rb b/lib/api.rb
index 848b806..a4d97c6 100644
--- a/lib/api.rb
+++ b/lib/api.rb
@@ -57,6 +57,6 @@ not_found do
   halt_with_message 404, 'Not found'
 end
 
-error Quote::Invalid do
+error ArgumentError do
   halt_with_message 422, env['sinatra.error'].message.capitalize
 end
diff --git a/lib/quote.rb b/lib/quote.rb
index 229393d..6d35c56 100644
--- a/lib/quote.rb
+++ b/lib/quote.rb
@@ -4,8 +4,6 @@ require 'currency'
 class Quote
   include Virtus.value_object
 
-  NotValid = Class.new(ArgumentError)
-
   DEFAULT_BASE = 'EUR'
 
   values do
@@ -32,7 +30,7 @@ class Quote
 
   def date=(date)
     current_date = Currency.current_date_before(date)
-    fail NotValid, 'Date too old' unless current_date
+    fail ArgumentError, 'Date too old' unless current_date
 
     super current_date
   end
@@ -54,7 +52,7 @@ class Quote
   def find_rebased_rates
     rates = find_default_rates
     denominator = rates.update(DEFAULT_BASE => 1.0).delete(base)
-    fail NotValid, 'Invalid base' unless denominator
+    fail ArgumentError, 'Invalid base' unless denominator
     rates.each do |iso_code, rate|
       rates[iso_code] = round_rate(rate / denominator)
     end
diff --git a/spec/quote_spec.rb b/spec/quote_spec.rb
index 6834228..d0205f2 100644
--- a/spec/quote_spec.rb
+++ b/spec/quote_spec.rb
@@ -54,9 +54,7 @@ describe Quote do
     let(:quote) { Quote.new(base: 'FOO') }
 
     it 'fails' do
-      stub_rates 'USD' => 1.25 do |quote|
-        proc { quote.to_h }.must_raise Quote::NotValid
-      end
+      proc { quote.to_h }.must_raise ArgumentError
     end
   end
 
@@ -65,7 +63,7 @@ describe Quote do
 
     it 'fails' do
       Currency.stub :current_date_before, nil do
-        proc { quote }.must_raise Quote::NotValid
+        proc { quote }.must_raise ArgumentError
       end
     end
   end