diff --git a/lib/money/currency.rb b/lib/money/currency.rb
index a27759c9..53da2228 100644
--- a/lib/money/currency.rb
+++ b/lib/money/currency.rb
@@ -11,9 +11,13 @@ class UnknownCurrency < ArgumentError; end
 
     class << self
       def new(currency_iso)
-        raise UnknownCurrency, "Currency can't be blank" if currency_iso.nil? || currency_iso.to_s.empty?
-        iso = currency_iso.to_s.downcase
-        @@loaded_currencies[iso] || @@mutex.synchronize { @@loaded_currencies[iso] = super(iso) }
+        iso = currency_iso.to_s
+        return @@loaded_currencies[iso] if @@loaded_currencies.key?(iso)
+        raise UnknownCurrency, "Currency can't be blank" if iso.empty?
+        downcased = iso.downcase
+        @@mutex.synchronize do
+          @@loaded_currencies[iso] ||= @@loaded_currencies[downcased] ||= super(downcased)
+        end
       end
       alias_method :find!, :new