diff --git a/.document b/.document
deleted file mode 100644
index ecf3673..0000000
--- a/.document
+++ /dev/null
@@ -1,5 +0,0 @@
-README.rdoc
-lib/**/*.rb
-bin/*
-features/**/*.feature
-LICENSE
diff --git a/.rvmrc b/.rvmrc
new file mode 100644
index 0000000..e182e8a
--- /dev/null
+++ b/.rvmrc
@@ -0,0 +1 @@
+rvm --create use ruby-1.8.7@simple_currency > /dev/null
diff --git a/lib/simple_currency/currency_convertible.rb b/lib/simple_currency/currency_convertible.rb
index 0e49a2b..4fe2cff 100644
--- a/lib/simple_currency/currency_convertible.rb
+++ b/lib/simple_currency/currency_convertible.rb
@@ -35,8 +35,10 @@ def _to(target)
 
       # If not, perform a call to the api
       json_response = call_api(original, target, amount)
-      return nil unless json_response
-      result = sprintf("%.2f", JSON.parse(json_response)["result"]["value"]).to_f
+      return nil unless json_response && parsed_response = JSON.parse(json_response)
+      raise parsed_response["message"] if parsed_response["status"] != "ok"
+
+      result = sprintf("%.2f", parsed_response["result"]["value"]).to_f
 
       # Cache exchange rate for today only
       Rails.cache.write("#{original}_#{target}_#{Time.now.to_a[3..5].join('-')}", calculate_rate(amount,result)) if defined?(Rails)
@@ -55,7 +57,7 @@ def _to(target)
     end
 
     def check_cache(original, target, amount)
-      if rate = ::Rails.cache.read("#{original}_#{target}_#{Time.now.to_a[3..5].join('-')}")
+      if rate = Rails.cache.read("#{original}_#{target}_#{Time.now.to_a[3..5].join('-')}")
         result = (amount * rate).to_f
         return result = (result * 100).round.to_f / 100
       end
diff --git a/spec/simple_currency_spec.rb b/spec/simple_currency_spec.rb
index 08289e2..702cd01 100644
--- a/spec/simple_currency_spec.rb
+++ b/spec/simple_currency_spec.rb
@@ -2,9 +2,13 @@
 
 describe "SimpleCurrency" do
 
-  def mock_uri(from_currency, to_currency, amount, result)
+  def mock_uri(from_currency, to_currency, amount, result, options = {})
     args = [from_currency, to_currency, amount]
+
     response = "{\"result\":{\"value\":#{result},\"target\":\"#{to_currency}\",\"base\":\"#{from_currency}\"},\"status\":\"ok\"}"
+
+    response = "{\"message\":\"#{options[:fail_with]}\", \"status\":\"fail\"\}" if options[:fail_with]
+
     FakeWeb.register_uri(:get, "http://xurrency.com/api/#{args.join('/')}", :body => response)
   end
 
@@ -29,6 +33,14 @@ def mock_uri(from_currency, to_currency, amount, result)
     8.should respond_to(:to_eur)
   end
 
+  it "raises any error returned by the api call" do
+    mock_uri('usd', 'xxx', 1, 1.5, :fail_with => "The currencies are not valid")
+    mock_uri('usd', 'eur', 1_000_000_000, 1.5, :fail_with => "The amount should be between 0 and 999999999")
+
+    expect {1.usd.to_xxx}.to raise_error("The currencies are not valid")
+    expect {1_000_000_000.usd.to_eur}.to raise_error("The amount should be between 0 and 999999999")
+  end
+
   context "when Rails is present" do
 
     before(:all) do
@@ -50,13 +62,15 @@ def mock_uri(from_currency, to_currency, amount, result)
     it "ensures the cache is valid only for today" do
       now = Time.parse('2010-08-30')
 
+      Time.stub(:now).and_return(now)
+
       Rails.stub_chain("cache.write").and_return(true)
       Rails.stub_chain("cache.read").with('usd_eur_30-8-2010').and_return(1.5)
 
       mock_uri('usd', 'eur', 1, 1.5)
       1.usd.to_eur.should == 1.5
 
-      Time.stub(:now).and_return(now + 86400) # Tomorrow
+      Time.stub(:now).and_return(now + 86400) # One day later
       Rails.stub_chain("cache.read").with('usd_eur_31-8-2010').and_return(nil)
 
       # Exchange rate has changed next day, so forget cache rate!