diff --git a/swift/common/middleware/formpost.py b/swift/common/middleware/formpost.py
index b7df8eace5..f2ec952d2f 100644
--- a/swift/common/middleware/formpost.py
+++ b/swift/common/middleware/formpost.py
@@ -312,7 +312,9 @@ class FormPost(object):
                     _parse_attrs(env.get('CONTENT_TYPE') or '')
                 if content_type == 'multipart/form-data' and \
                         'boundary' in attrs:
-                    env['HTTP_USER_AGENT'] += ' FormPost'
+                    http_user_agent = "%s FormPost" % (
+                        env.get('HTTP_USER_AGENT', ''))
+                    env['HTTP_USER_AGENT'] = http_user_agent.strip()
                     status, headers, body = self._translate_form(
                         env, attrs['boundary'])
                     start_response(status, headers)
diff --git a/test/unit/common/middleware/test_formpost.py b/test/unit/common/middleware/test_formpost.py
index c26ffd7f59..8bad58687b 100644
--- a/test/unit/common/middleware/test_formpost.py
+++ b/test/unit/common/middleware/test_formpost.py
@@ -304,7 +304,7 @@ class TestFormPost(unittest.TestCase):
         return req
 
     def _make_sig_env_body(self, path, redirect, max_file_size, max_file_count,
-                           expires, key):
+                           expires, key, user_agent=True):
         sig = hmac.new(
             key,
             '%s\n%s\n%s\n%s\n%s' % (
@@ -379,6 +379,9 @@ class TestFormPost(unittest.TestCase):
             'wsgi.url_scheme': 'http',
             'wsgi.version': (1, 0),
         }
+        if user_agent is False:
+            del env['HTTP_USER_AGENT']
+
         return sig, env, body
 
     def test_passthrough(self):
@@ -1173,6 +1176,26 @@ class TestFormPost(unittest.TestCase):
             in body)
         self.assertEquals(len(self.app.requests), 0)
 
+    def test_formpost_without_useragent(self):
+        key = 'abc'
+        sig, env, body = self._make_sig_env_body(
+            '/v1/AUTH_test/container', 'http://redirect', 1024, 10,
+            int(time() + 86400), key, user_agent=False)
+        env['wsgi.input'] = StringIO('\r\n'.join(body))
+        env['swift.cache'] = FakeMemcache()
+        env['swift.cache'].set('temp-url-key/AUTH_test', key)
+        self.app = FakeApp(iter([('201 Created', {}, ''),
+                                 ('201 Created', {}, '')]))
+        self.auth = tempauth.filter_factory({})(self.app)
+        self.formpost = formpost.filter_factory({})(self.auth)
+
+        def start_response(s, h, e=None):
+            pass
+        body = ''.join(self.formpost(env, start_response))
+        self.assertTrue('User-Agent' in self.app.requests[0].headers)
+        self.assertEquals(self.app.requests[0].headers['User-Agent'],
+                          'FormPost')
+
     def test_redirect(self):
         key = 'abc'
         sig, env, body = self._make_sig_env_body(