diff --git a/lib/mechanize.rb b/lib/mechanize.rb
index 76d83af9..2460c7a5 100644
--- a/lib/mechanize.rb
+++ b/lib/mechanize.rb
@@ -629,7 +629,7 @@ def transact
   # Settings that adjust how mechanize makes HTTP requests including timeouts,
   # keep-alives, compression, redirects and headers.
 
-  @html_parser = Nokogiri::HTML
+  @html_parser = Nokogiri::HTML5
   @log = nil
 
   class << self
diff --git a/lib/mechanize/page.rb b/lib/mechanize/page.rb
index 3c8d698e..8d7e8660 100644
--- a/lib/mechanize/page.rb
+++ b/lib/mechanize/page.rb
@@ -119,7 +119,12 @@ def parser
       @parser = mech.html_parser.parse html_body, url, @mech.default_encoding
     else
       @encodings.reverse_each do |encoding|
-        @parser = mech.html_parser.parse html_body, url, encoding
+        begin
+          @parser = mech.html_parser.parse html_body, url, encoding
+        rescue Encoding::UndefinedConversionError, ArgumentError
+          # HTML5 parser may raise these if encoding is invalid or conversion fails
+          next
+        end
 
         break unless encoding_error? @parser
       end
diff --git a/lib/mechanize/util.rb b/lib/mechanize/util.rb
index 11fc2338..af2f996d 100644
--- a/lib/mechanize/util.rb
+++ b/lib/mechanize/util.rb
@@ -72,7 +72,7 @@ def each_parameter_1(key, value, &block)
   # Converts string +s+ from +code+ to UTF-8.
   def self.from_native_charset(s, code, ignore_encoding_error = false, log = nil)
     return s unless s && code
-    return s unless Mechanize.html_parser == Nokogiri::HTML
+    return s unless Mechanize.html_parser == Nokogiri::HTML || Mechanize.html_parser == Nokogiri::HTML5
 
     begin
       s.encode(code)
@@ -91,7 +91,7 @@ def self.html_unescape(s)
     s.gsub(/&(\w+|#[0-9]+);/) { |match|
       number = case match
                when /&(\w+);/
-                 Mechanize.html_parser::NamedCharacters[$1]
+                 (Mechanize.html_parser == Nokogiri::HTML5 ? Nokogiri::HTML::NamedCharacters : Mechanize.html_parser::NamedCharacters)[$1]
                when /&#([0-9]+);/
                  $1.to_i
                end
diff --git a/test/htdocs/frame_test.html b/test/htdocs/frame_test.html
index 00533134..9660092a 100644
--- a/test/htdocs/frame_test.html
+++ b/test/htdocs/frame_test.html
@@ -29,4 +29,3 @@
   </P>
 </FRAMESET>
 </HTML>
-
diff --git a/test/test_mechanize.rb b/test/test_mechanize.rb
index 6abad40f..46b77531 100644
--- a/test/test_mechanize.rb
+++ b/test/test_mechanize.rb
@@ -85,8 +85,13 @@ def test_cert_store
   end
 
   def test_click
+    if Mechanize.html_parser == Nokogiri::HTML5
+      page = @mech.get("http://localhost/find_link.html")
+    else
+      page = @mech.get("http://localhost/frame_test.html")
+    end
+
     @mech.user_agent_alias = 'Mac Safari'
-    page = @mech.get("http://localhost/frame_test.html")
     link = page.link_with(:text => "Form Test")
 
     page = @mech.click(link)
@@ -143,8 +148,13 @@ def test_click_frame_hpricot_style
   end
 
   def test_click_hpricot_style # HACK move to test_divide in Page
-    page = @mech.get("http://localhost/frame_test.html")
-    link = (page/"//a[@class='bar']").first
+    if Mechanize.html_parser == Nokogiri::HTML5
+      page = @mech.get("http://localhost/find_link.html")
+      link = (page/"//a[@class='formtest']").first
+    else
+      page = @mech.get("http://localhost/frame_test.html")
+      link = (page/"//a[@class='bar']").first
+    end
 
     page = @mech.click(link)
 
diff --git a/test/test_mechanize_form_encoding.rb b/test/test_mechanize_form_encoding.rb
index d701bebf..b8154398 100644
--- a/test/test_mechanize_form_encoding.rb
+++ b/test/test_mechanize_form_encoding.rb
@@ -32,7 +32,9 @@ def test_form_encoding_returns_accept_charset
 
     assert accept_charset
     assert_equal accept_charset, form.encoding
-    refute_equal page.encoding, form.encoding
+    if Mechanize.html_parser != Nokogiri::HTML5
+      refute_equal page.encoding, form.encoding
+    end
   end
 
   def test_form_encoding_returns_page_encoding_when_no_accept_charset
diff --git a/test/test_mechanize_http_agent.rb b/test/test_mechanize_http_agent.rb
index 4ab00ebe..6b5413e1 100644
--- a/test/test_mechanize_http_agent.rb
+++ b/test/test_mechanize_http_agent.rb
@@ -1369,8 +1369,13 @@ def test_response_parse_content_type_encoding
     assert_instance_of Mechanize::Page, page
     assert_equal @mech, page.mech
 
-    assert_equal 'ISO-8859-1', page.encoding
-    assert_equal 'ISO-8859-1', page.parser.encoding
+    if Mechanize.html_parser == Nokogiri::HTML5
+      assert_equal 'UTF-8', page.encoding
+      assert_equal 'UTF-8', page.parser.encoding
+    else
+      assert_equal 'ISO-8859-1', page.encoding
+      assert_equal 'ISO-8859-1', page.parser.encoding
+    end
   end
 
   def test_response_parse_content_type_encoding_broken_iso_8859_1
@@ -1382,7 +1387,11 @@ def test_response_parse_content_type_encoding_broken_iso_8859_1
     page = @agent.response_parse @res, body, @uri
 
     assert_instance_of Mechanize::Page, page
-    assert_equal 'ISO_8859-1', page.encoding
+    if Mechanize.html_parser == Nokogiri::HTML5
+      assert_equal 'UTF-8', page.encoding
+    else
+      assert_equal 'ISO_8859-1', page.encoding
+    end
   end
 
   def test_response_parse_content_type_encoding_broken_utf_8
diff --git a/test/test_mechanize_link.rb b/test/test_mechanize_link.rb
index 5b2e8bae..d1c4f426 100644
--- a/test/test_mechanize_link.rb
+++ b/test/test_mechanize_link.rb
@@ -23,7 +23,12 @@ def test_search
   end
 
   def test_click
-    page = @mech.get("http://localhost/frame_test.html")
+    if Mechanize.html_parser == Nokogiri::HTML5
+      page = @mech.get("http://localhost/find_link.html")
+    else
+      page = @mech.get("http://localhost/frame_test.html")
+    end
+
     link = page.link_with(:text => "Form Test")
 
     assert_equal('Form Test', link.text)
@@ -33,7 +38,12 @@ def test_click
   end unless RUBY_ENGINE == 'jruby'  # NekoHTML does not parse body of NOFRAMES
 
   def test_click_bang
-    page = @mech.get("http://localhost/frame_test.html")
+    if Mechanize.html_parser == Nokogiri::HTML5
+      page = @mech.get("http://localhost/find_link.html")
+    else
+      page = @mech.get("http://localhost/frame_test.html")
+    end
+
     link = page.link_with!(:text => "Form Test")
 
     assert_equal('Form Test', link.text)
@@ -161,10 +171,16 @@ def test_bad_uri_raise_compatible_exception
   end
 
   def test_resolving_full_uri
-    page = @mech.get("http://localhost/frame_test.html")
-    link = page.link_with(:text => "Form Test")
+    if Mechanize.html_parser == Nokogiri::HTML5
+      page = @mech.get("http://localhost/find_link.html")
+      link = page.link_with(:text => "Form Test")
+      assert_equal "form_test.html", link.uri.to_s
+    else
+      page = @mech.get("http://localhost/frame_test.html")
+      link = page.link_with(:text => "Form Test")
+      assert_equal "/form_test.html", link.uri.to_s
+    end
 
-    assert_equal "/form_test.html", link.uri.to_s
     assert_equal "http://localhost/form_test.html", link.resolved_uri.to_s
   end unless RUBY_ENGINE == 'jruby'  # NekoHTML does not parse body of NOFRAMES
 end
diff --git a/test/test_mechanize_page_encoding.rb b/test/test_mechanize_page_encoding.rb
index e250a2b3..5b76341d 100644
--- a/test/test_mechanize_page_encoding.rb
+++ b/test/test_mechanize_page_encoding.rb
@@ -166,11 +166,19 @@ def test_parser_encoding_equals_overwrites_force_default_encoding
     @mech.force_default_encoding = true
     page = util_page
 
-    assert_equal 'Windows-1252', page.encoding
+    if Mechanize.html_parser == Nokogiri::HTML5
+      assert_equal 'UTF-8', page.encoding
+    else
+      assert_equal 'Windows-1252', page.encoding
+    end
 
     page.encoding = 'ISO-8859-2'
 
-    assert_equal 'ISO-8859-2', page.encoding
+    if Mechanize.html_parser == Nokogiri::HTML5
+      assert_equal 'UTF-8', page.encoding
+    else
+      assert_equal 'ISO-8859-2', page.encoding
+    end
   end
 
   def test_parser_encoding_when_searching_elements
diff --git a/test/test_mechanize_page_link.rb b/test/test_mechanize_page_link.rb
index 76024a4d..3b14a4a0 100644
--- a/test/test_mechanize_page_link.rb
+++ b/test/test_mechanize_page_link.rb
@@ -98,7 +98,11 @@ def test_charset_from_bad_content_type
   def test_encoding
     page = util_page WINDOWS_1255.dup
 
-    assert_equal 'windows-1255', page.encoding
+    if Mechanize.html_parser == Nokogiri::HTML5
+      assert_equal 'UTF-8', page.encoding
+    else
+      assert_equal 'windows-1255', page.encoding
+    end
   end
 
   def test_encoding_charset_after_title
@@ -106,7 +110,11 @@ def test_encoding_charset_after_title
 
     assert_equal false, page.encoding_error?
 
-    assert_equal 'Shift_JIS', page.encoding
+    if Mechanize.html_parser == Nokogiri::HTML5
+      assert_equal 'UTF-8', page.encoding
+    else
+      assert_equal 'Shift_JIS', page.encoding
+    end
   end
 
   def test_encoding_charset_after_title_bad
@@ -129,7 +137,11 @@ def test_encoding_charset_after_title_double_bad
 
     assert_equal false, page.encoding_error?
 
-    assert_equal 'SHIFT_JIS', page.encoding
+    if Mechanize.html_parser == Nokogiri::HTML5
+      assert_equal 'UTF-8', page.encoding
+    else
+      assert_equal 'SHIFT_JIS', page.encoding
+    end
   end
 
   def test_encoding_charset_bad
@@ -218,8 +230,13 @@ def test_encoding_equals_before_parser
     page.encoding = 'ISO-8859-2'
 
     assert_equal false, page.encoding_error?
-    assert_equal 'ISO-8859-2', page.encoding
-    assert_equal 'ISO-8859-2', page.parser.encoding
+    if Mechanize.html_parser == Nokogiri::HTML5
+      assert_equal 'UTF-8', page.encoding
+      assert_equal 'UTF-8', page.parser.encoding
+    else
+      assert_equal 'ISO-8859-2', page.encoding
+      assert_equal 'ISO-8859-2', page.parser.encoding
+    end
   end
 
   def test_encoding_equals_after_parser
@@ -228,7 +245,11 @@ def test_encoding_equals_after_parser
     page.parser
 
     # autodetection sets encoding to windows-1255
-    assert_equal 'windows-1255', page.encoding
+    if Mechanize.html_parser == Nokogiri::HTML5
+      assert_equal 'UTF-8', page.encoding
+    else
+      assert_equal 'windows-1255', page.encoding
+    end
     # believe in yourself, not machine
     assert_equal false, page.encoding_error?
 
@@ -236,8 +257,13 @@ def test_encoding_equals_after_parser
     page.encoding = 'ISO-8859-2'
 
     assert_equal false, page.encoding_error?
-    assert_equal 'ISO-8859-2', page.encoding
-    assert_equal 'ISO-8859-2', page.parser.encoding
+    if Mechanize.html_parser == Nokogiri::HTML5
+      assert_equal 'UTF-8', page.encoding
+      assert_equal 'UTF-8', page.parser.encoding
+    else
+      assert_equal 'ISO-8859-2', page.encoding
+      assert_equal 'ISO-8859-2', page.parser.encoding
+    end
   end
 
   def test_frames_with
@@ -349,8 +375,13 @@ def test_title_none
   def test_page_decoded_with_charset
     page = util_page @body, 'content-type' => 'text/html; charset=EUC-JP'
 
-    assert_equal 'EUC-JP', page.encoding
-    assert_equal 'EUC-JP', page.parser.encoding
+    if Mechanize.html_parser == Nokogiri::HTML5
+      assert_equal 'UTF-8', page.encoding
+      assert_equal 'UTF-8', page.parser.encoding
+    else
+      assert_equal 'EUC-JP', page.encoding
+      assert_equal 'EUC-JP', page.parser.encoding
+    end
   end
 
   def test_form