diff --git a/lib/mail/multibyte/chars.rb b/lib/mail/multibyte/chars.rb
index f65e69d5f..14306d6b5 100644
--- a/lib/mail/multibyte/chars.rb
+++ b/lib/mail/multibyte/chars.rb
@@ -339,7 +339,7 @@ def limit(limit)
       # Example:
       #   'Laurent, où sont les tests ?'.mb_chars.upcase.to_s # => "LAURENT, OÙ SONT LES TESTS ?"
       def upcase
-        chars(Unicode.apply_mapping(@wrapped_string), :uppercase_mapping)
+        chars(Unicode.apply_mapping(@wrapped_string, :uppercase_mapping))
       end
 
       # Convert characters in the string to lowercase.
@@ -347,7 +347,7 @@ def upcase
       # Example:
       #   'VĚDA A VÝZKUM'.mb_chars.downcase.to_s # => "věda a výzkum"
       def downcase
-        chars(Unicode.apply_mapping(@wrapped_string), :lowercase_mapping)
+        chars(Unicode.apply_mapping(@wrapped_string, :lowercase_mapping))
       end
 
       # Converts the first character to uppercase and the remainder to lowercase.
diff --git a/spec/mail/multibyte_spec.rb b/spec/mail/multibyte_spec.rb
new file mode 100644
index 000000000..cff7079a5
--- /dev/null
+++ b/spec/mail/multibyte_spec.rb
@@ -0,0 +1,17 @@
+# encoding: utf-8
+require 'spec_helper'
+
+describe "multibyte/chars" do
+  Chars = Mail::Multibyte::Chars
+
+  it "should upcase" do
+    chars = Chars.new('Laurent, où sont les tests ?')
+    chars.upcase.should == "LAURENT, OÙ SONT LES TESTS ?"
+  end
+
+  it "should downcase" do
+    chars = Chars.new('VĚDA A VÝZKUM')
+    chars.downcase.should == "věda a výzkum"
+  end
+end
+