diff --git a/lib/mongo/util/uri_parser.rb b/lib/mongo/util/uri_parser.rb
index de04534..24b3d02 100644
--- a/lib/mongo/util/uri_parser.rb
+++ b/lib/mongo/util/uri_parser.rb
@@ -16,6 +16,8 @@
 # limitations under the License.
 # ++
 
+require 'cgi'
+
 module Mongo
   class URIParser
 
@@ -260,8 +262,12 @@ module Mongo
 
       return if string_opts.empty? && extra_opts.empty?
 
-      opts = string_opts.split(/&|;/).inject({}) do |memo, kv|
-        key, value = kv.split('=')
+      if string_opts.include?(';') and string_opts.include?('&')
+        raise MongoArgumentError, "must not mix URL separators ; and &"
+      end
+
+      opts = CGI.parse(string_opts).inject({}) do |memo, (key, value)|
+        value = value[0]
         memo[key.downcase.to_sym] = value.strip.downcase
         memo
       end
diff --git a/test/uri_test.rb b/test/uri_test.rb
index 2a7f279..b5eb154 100644
--- a/test/uri_test.rb
+++ b/test/uri_test.rb
@@ -79,11 +79,19 @@ class URITest < Test::Unit::TestCase
     assert parser.safe
   end
 
-  #def test_opts_made_invalid_by_mixed_separators
-  #  assert_raise_error ArgumentError, "invalid data of application/x-www-form-urlencoded (replicaset=foo;bar&slaveok=true&safe=true)" do
-  #    Mongo::URIParser.new('mongodb://localhost:27018?replicaset=foo;bar&slaveok=true&safe=true')
-  #  end
-  #end
+  def test_opts_with_uri_encoded_stuff
+    parser = Mongo::URIParser.new('mongodb://localhost:27018?connect=%64%69%72%65%63%74&slaveok=%74%72%75%65&safe=true')
+    assert_equal 'direct', parser.connect
+    assert parser.direct?
+    assert parser.slaveok
+    assert parser.safe
+  end
+
+  def test_opts_made_invalid_by_mixed_separators
+    assert_raise_error MongoArgumentError, "must not mix URL separators ; and &" do
+      Mongo::URIParser.new('mongodb://localhost:27018?replicaset=foo;bar&slaveok=true&safe=true')
+    end
+  end
 
   def test_opts_safe
     parser = Mongo::URIParser.new('mongodb://localhost:27018?safe=true;w=2;journal=true;fsync=true;wtimeoutMS=200')