diff --git a/lib/mongo/util/uri_parser.rb b/lib/mongo/util/uri_parser.rb
index fdee374..8e26206 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\d]+):([-_\w\d]+)@)?([-.\w\d]+)(:([\w\d]+))?(\/([-\d\w]+))?/
+    MONGODB_URI_MATCHER = /(([-_.\w\d]+):([^@]+)@)?([-.\w\d]+)(:([\w\d]+))?(\/([-\d\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]
@@ -57,6 +57,8 @@ module Mongo
     # Parse a MongoDB URI. This method is used by Connection.from_uri.
     # Returns an array of nodes and an array of db authorizations, if applicable.
     #
+    # Note: passwords can contain any character except for a ','.
+    #
     # @core connections
     def initialize(string)
       if string =~ /^mongodb:\/\//
diff --git a/test/uri_test.rb b/test/uri_test.rb
index d2d9acb..84e1b1c 100644
--- a/test/uri_test.rb
+++ b/test/uri_test.rb
@@ -26,6 +26,22 @@ class TestThreading < Test::Unit::TestCase
     assert_equal 27017, parser.nodes[1][1]
   end
 
+  def test_complex_passwords
+    parser = Mongo::URIParser.new('mongodb://bob:secret.word@a.example.com:27018/test')
+    assert_equal "bob", parser.auths[0]["username"]
+    assert_equal "secret.word", parser.auths[0]["password"]
+
+    parser = Mongo::URIParser.new('mongodb://bob:s-_3#%R.t@a.example.com:27018/test')
+    assert_equal "bob", parser.auths[0]["username"]
+    assert_equal "s-_3#%R.t", parser.auths[0]["password"]
+  end
+
+  def test_passwords_contain_no_commas
+    assert_raise MongoArgumentError do
+      Mongo::URIParser.new('mongodb://bob:a,b@a.example.com:27018/test')
+    end
+  end
+
   def test_multiple_uris_with_auths
     parser = Mongo::URIParser.new('mongodb://bob:secret@a.example.com:27018/test,joe:secret2@b.example.com/test2')
     assert_equal 2, parser.nodes.length