diff --git a/lib/haml/buffer.rb b/lib/haml/buffer.rb
index 04531e80..40be89c6 100644
--- a/lib/haml/buffer.rb
+++ b/lib/haml/buffer.rb
@@ -115,7 +115,7 @@ module Haml
     # that can then be merged with another attributes hash.
     def parse_class_and_id(list)
       attributes = {}
-      list.scan(/([#.])([-a-zA-Z_()]+)/) do |type, property|
+      list.scan(/([#.])([-_a-zA-Z0-9]+)/) do |type, property|
         case type
         when '.'
           if attributes[:class]
diff --git a/test/results/tag_parsing.xhtml b/test/results/tag_parsing.xhtml
index c32373af..c1d694c4 100644
--- a/test/results/tag_parsing.xhtml
+++ b/test/results/tag_parsing.xhtml
@@ -18,9 +18,9 @@
   <div class='foo-bar'>b</div>
   <div class='foo_bar'>c</div>
   <div class='FOOBAR'>d</div>
-  <div class='foo'>e</div>
-  <div>f</div>
-  <div class='foo'>g</div>
+  <div class='foo16'>e</div>
+  <div class='123'>f</div>
+  <div class='foo2u'>g</div>
 </div>
 <div class='broken'>
   <foo><{ :a => :b }</foo>