Only turn values to arrays if requested with [] naming. Otherwise use the last provided value for the field.

lib/capybara/driver/rack_test_driver.rb

@@ -108,13 +108,14 @@ class Capybara::Driver::RackTest
     
     def merge_param!(params, key, value)
       collection = key.sub!(/\[\]$/, '')
-      case params[key]
-      when nil
-        params[key] = collection ? [value] : value
-      when Array
-        params[key] << value
+      if collection
+        if params[key]
+          params[key] << value
+        else
+          params[key] = [value]
+        end
       else
-        params[key] = [params[key], value]
+        params[key] = value
       end
     end
   end

spec/session_spec.rb

@@ -67,6 +67,14 @@ shared_examples_for "session" do
       @session.visit('/form')
     end
 
+    context "with multiple values with the same name" do
+      it "should use the latest given value" do
+        @session.check('Terms of Use')
+        @session.click_button('awesome')
+        extract_results(@session)['terms_of_use'].should == '1'
+      end
+    end
+
     context "with value given on a submit button" do
       before do
         @session.click_button('awesome')

spec/views/form.erb

@@ -25,7 +25,13 @@
     <label for="form_password">Password</label>
     <input type="password" name="form[password]" value="seeekrit" id="form_password"/>
   </p>
-  
+
+  <p>
+    <label for="form_terms_of_use">Terms of Use</label>
+    <input type="hidden" name="form[terms_of_use]" value="0" id="form_terms_of_use_default">
+    <input type="checkbox" name="form[terms_of_use]" value="1" id="form_terms_of_use">
+  </p>
+
   <p>
     <label for="form_image">Image</label>
     <input type="file" name="form[image]" id="form_image"/>