diff --git a/activesupport/lib/active_support/multibyte/chars.rb b/activesupport/lib/active_support/multibyte/chars.rb
index 51b870de8cdeaeff372d0cff8dbeb982e3df3a5b..d372b0ab1ff00535bb81eb62003929f268d59369 100644
--- a/activesupport/lib/active_support/multibyte/chars.rb
+++ b/activesupport/lib/active_support/multibyte/chars.rb
@@ -665,6 +665,11 @@ def tidy_bytes(string)
         def translate_offset(byte_offset) #:nodoc:
           return nil if byte_offset.nil?
           return 0   if @wrapped_string == ''
+          
+          if @wrapped_string.respond_to?(:force_encoding)
+            @wrapped_string = @wrapped_string.dup.force_encoding(Encoding::ASCII_8BIT)
+          end
+          
           begin
             @wrapped_string[0...byte_offset].unpack('U*').length
           rescue ArgumentError => e
diff --git a/activesupport/test/multibyte_chars_test.rb b/activesupport/test/multibyte_chars_test.rb
index fc7b5e50819d0490475c566d907ee801f51e9a6f..4ff74abf61cd90e47a0602ba5271318d09923ccf 100644
--- a/activesupport/test/multibyte_chars_test.rb
+++ b/activesupport/test/multibyte_chars_test.rb
@@ -100,15 +100,14 @@ class MultibyteCharsUTF8BehaviourTest < Test::Unit::TestCase
   def setup
     @chars = UNICODE_STRING.dup.mb_chars
 
-    # NEWLINE, SPACE, EM SPACE
-    @whitespace = "\n#{[32, 8195].pack('U*')}"
-
-    # Ruby 1.9 doesn't recognize EM SPACE as whitespace!
-    if @whitespace.respond_to?(:force_encoding)
-      @whitespace.slice!(2)
-      @whitespace.force_encoding(Encoding::UTF_8)
+    if RUBY_VERSION < '1.9'
+      # Multibyte support all kinds of whitespace (ie. NEWLINE, SPACE, EM SPACE)
+      @whitespace = "\n\t#{[32, 8195].pack('U*')}"
+    else
+      # Ruby 1.9 only supports basic whitespace
+      @whitespace = "\n\t ".force_encoding(Encoding::UTF_8)
     end
-
+    
     @byte_order_mark = [65279].pack('U')
   end
 
@@ -497,28 +496,27 @@ def test_capitalize_should_be_unicode_aware
   end
 
   def test_limit_should_not_break_on_blank_strings
-    chars = ''.mb_chars
-    
-    assert_equal '', chars.limit(0)
-    assert_equal '', chars.limit(1)
+    example = chars('')
+    assert_equal example, example.limit(0)
+    assert_equal example, example.limit(1)
   end
 
   def test_limit_should_work_on_a_multibyte_string
-    chars = UNICODE_STRING.mb_chars
+    example = chars(UNICODE_STRING)
+    bytesize = UNICODE_STRING.respond_to?(:bytesize) ? UNICODE_STRING.bytesize : UNICODE_STRING.size
     
-    assert_equal UNICODE_STRING, chars.limit(UNICODE_STRING.length)
-    assert_equal '', chars.limit(0)
-    assert_equal '', chars.limit(1)
-    assert_equal 'こ', chars.limit(3)
-    assert_equal 'こに', chars.limit(6)
-    assert_equal 'こに', chars.limit(8)
-    assert_equal 'こにち', chars.limit(9)
-    assert_equal 'こにちわ', chars.limit(50)
+    assert_equal UNICODE_STRING, example.limit(bytesize)
+    assert_equal '', example.limit(0)
+    assert_equal '', example.limit(1)
+    assert_equal 'こ', example.limit(3)
+    assert_equal 'こに', example.limit(6)
+    assert_equal 'こに', example.limit(8)
+    assert_equal 'こにち', example.limit(9)
+    assert_equal 'こにちわ', example.limit(50)
   end
 
   def test_limit_should_work_on_an_ascii_string
-    ascii = ASCII_STRING.mb_chars
-    
+    ascii = chars(ASCII_STRING)
     assert_equal ASCII_STRING, ascii.limit(ASCII_STRING.length)
     assert_equal '', ascii.limit(0)
     assert_equal 'o', ascii.limit(1)
@@ -528,12 +526,12 @@ def test_limit_should_work_on_an_ascii_string
   end
 
   def test_limit_should_keep_under_the_specified_byte_limit
-    chars = UNICODE_STRING.mb_chars
+    example = chars(UNICODE_STRING)
     (1..UNICODE_STRING.length).each do |limit|
-      assert chars.limit(limit).to_s.length <= limit
+      assert example.limit(limit).to_s.length <= limit
     end
   end
-
+  
   def test_composition_exclusion_is_set_up_properly
     # Normalization of DEVANAGARI LETTER QA breaks when composition exclusion isn't used correctly
     qa = [0x915, 0x93c].pack('U*')
@@ -647,9 +645,9 @@ def string_from_classes(classes)
 
 class MultibyteInternalsTest < ActiveSupport::TestCase
   include MultibyteTestHelpers
-  
+
   test "Chars translates a character offset to a byte offset" do
-    chars = "Puisque c'était son erreur, il m'a aidé".mb_chars
+    example = chars("Puisque c'était son erreur, il m'a aidé")
     [
       [0, 0],
       [3, 3],
@@ -657,7 +655,7 @@ class MultibyteInternalsTest < ActiveSupport::TestCase
       [14, 13],
       [41, 39]
     ].each do |byte_offset, character_offset|
-      assert_equal character_offset, chars.send(:translate_offset, byte_offset),
+      assert_equal character_offset, example.send(:translate_offset, byte_offset),
         "Expected byte offset #{byte_offset} to translate to #{character_offset}"
     end
   end