diff --git a/lib/sanitize.rb b/lib/sanitize.rb
index ebc045e0..f4c479ec 100644
--- a/lib/sanitize.rb
+++ b/lib/sanitize.rb
@@ -144,7 +144,7 @@ module Sanitize
                     node.attributes.delete_if { |attr,v| !ALLOWED_ATTRIBUTES.include?(attr) }
                     ATTR_VAL_IS_URI.each do |attr|
                       val_unescaped = CGI.unescapeHTML(node.attributes[attr].to_s).gsub(/[\000-\040\177-\240]+/,'').downcase
-                      if val_unescaped =~ /^[+-.\w]+:/ and !ALLOWED_PROTOCOLS.include?(val_unescaped.split(':')[0]) 
+                      if val_unescaped =~ /^[a-z0-9][-+.a-z0-9]*:/ and !ALLOWED_PROTOCOLS.include?(val_unescaped.split(':')[0]) 
                         node.attributes.delete attr 
                       end
                     end