diff --git a/lib/mongo/util/uri_parser.rb b/lib/mongo/util/uri_parser.rb
index 9336c93..b2af56f 100644
--- a/lib/mongo/util/uri_parser.rb
+++ b/lib/mongo/util/uri_parser.rb
@@ -20,7 +20,7 @@ module Mongo
   class URIParser
 
     DEFAULT_PORT = 27017
-    MONGODB_URI_MATCHER = /(([-.\w]+):([^@,]+)@)?((?:(?:[-.\w]+)(?::(?:[\w]+))?,?)+)(\/([-\w]+))?/
+    MONGODB_URI_MATCHER = /(([-.\w:]+):([^@,]+)@)?((?:(?:[-.\w]+)(?::(?:[\w]+))?,?)+)(\/([-\w]+))?/
     MONGODB_URI_SPEC = "mongodb://[username:password@]host1[:port1][,host2[:port2],...[,hostN[:portN]]][/database]"
     SPEC_ATTRS = [:nodes, :auths]
     OPT_ATTRS  = [:connect, :replicaset, :slaveok, :safe, :w, :wtimeout, :fsync]
diff --git a/test/uri_test.rb b/test/uri_test.rb
index 0d17d38..01df2e6 100644
--- a/test/uri_test.rb
+++ b/test/uri_test.rb
@@ -36,6 +36,11 @@ class TestThreading < Test::Unit::TestCase
     assert_equal "s-_3#%R.t", parser.auths[0]["password"]
   end
 
+  def test_complex_usernames
+    parser = Mongo::URIParser.new('mongodb://b:ob:secret.word@a.example.com:27018/test')
+    assert_equal "b:ob", parser.auths[0]["username"]
+  end
+
   def test_passwords_contain_no_commas
     assert_raise MongoArgumentError do
       Mongo::URIParser.new('mongodb://bob:a,b@a.example.com:27018/test')