diff --git a/Rakefile b/Rakefile
index d7197692..69f18bb7 100644
--- a/Rakefile
+++ b/Rakefile
@@ -5,7 +5,7 @@ require 'rspec/core'
 require "rspec/core/rake_task"
 
 RSpec::Core::RakeTask.new do |t|
-  t.pattern = "./**/*_spec.rb"
+  t.pattern = "spec/**/*_spec.rb"
   t.ruby_opts = "-w"
 end
 
diff --git a/lib/rack/test.rb b/lib/rack/test.rb
index 8877e7f3..e33bf1b7 100644
--- a/lib/rack/test.rb
+++ b/lib/rack/test.rb
@@ -209,8 +209,8 @@ def env_for(path, env)
           # merge :params with the query string
           if params = env[:params]
             params = parse_nested_query(params) if params.is_a?(String)
-            params.update(parse_nested_query(uri.query))
-            uri.query = build_nested_query(params)
+
+            uri.query = [uri.query, build_nested_query(params)].compact.join("&")
           end
         elsif !env.has_key?(:input)
           env["CONTENT_TYPE"] ||= "application/x-www-form-urlencoded"
diff --git a/spec/rack/test_spec.rb b/spec/rack/test_spec.rb
index ba862b28..377eb1f9 100644
--- a/spec/rack/test_spec.rb
+++ b/spec/rack/test_spec.rb
@@ -127,6 +127,11 @@
       last_request.query_string.should == "a=1&b=2&c=3&e=4&d=5+%20"
     end
 
+    it "does not overwrite multiple query string keys" do
+      request "/foo?a=1&a=2", :params => { :bar => 1 }
+      last_request.query_string.should == "a=1&a=2&bar=1"
+    end
+
     it "accepts params and builds url encoded params for POST requests" do
       request "/foo", :method => :post, :params => {:foo => {:bar => "1"}}
       last_request.env["rack.input"].read.should == "foo[bar]=1"