diff --git a/src/gam.py b/src/gam.py
index ffc21204..1ee3a344 100755
--- a/src/gam.py
+++ b/src/gam.py
@@ -80,6 +80,26 @@ Go to the following link in your browser:
     {address}
 """
 
+# Override and wrap google_auth_httplib2.Request.__call__ so that the GAM
+# user-agent string is inserted into HTTP request headers.
+google_auth_httplib2_request_call = google_auth_httplib2.Request.__call__
+def _request_with_user_agent(self, *args, **kwargs):
+  """Inserts the GAM user-agent header in all google_auth_httplib2 requests."""
+  GAM_USER_AGENT = GAM_INFO
+
+  if kwargs.get('headers') is not None:
+    if kwargs['headers'].get('user-agent'):
+      # Save the existing user-agent header and tack on the GAM user-agent.
+      kwargs['headers']['user-agent'] = '%s %s' % (
+          GAM_USER_AGENT, kwargs.headers['user-agent'])
+    else:
+      kwargs['headers']['user-agent'] = GAM_USER_AGENT
+  else:
+    kwargs['headers'] = {'user-agent': GAM_USER_AGENT}
+  return google_auth_httplib2_request_call(self, *args, **kwargs)
+
+google_auth_httplib2.Request.__call__ = _request_with_user_agent
+
 def showUsage():
   doGAMVersion(checkForArgs=False)
   print u'''
@@ -1064,10 +1084,10 @@ def buildGAPIServiceObject(api, act_as, showAuthError=True):
   GM_Globals[GM_CURRENT_API_USER] = act_as
   GM_Globals[GM_CURRENT_API_SCOPES] = API_SCOPE_MAPPING[api]
   credentials = getSvcAcctCredentials(GM_Globals[GM_CURRENT_API_SCOPES], act_as)
-  request = google_auth_httplib2.Request(http, user_agent=GAM_INFO)
+  request = google_auth_httplib2.Request(http)
   try:
     credentials.refresh(request)
-    service._http = google_auth_httplib2.AuthorizedHttp(credentials, http=http, user_agent=GAM_INFO)
+    service._http = google_auth_httplib2.AuthorizedHttp(credentials, http=http)
   except httplib2.ServerNotFoundError as e:
     systemErrorExit(4, e)
   except google.auth.exceptions.RefreshError as e:
@@ -1129,7 +1149,7 @@ def doCheckServiceAccount(users):
     for scope in all_scopes:
       try:
         credentials = getSvcAcctCredentials([scope], user)
-        request = google_auth_httplib2.Request(httplib2.Http(disable_ssl_certificate_validation=GC_Values[GC_NO_VERIFY_SSL]), user_agent=GAM_INFO)
+        request = google_auth_httplib2.Request(httplib2.Http(disable_ssl_certificate_validation=GC_Values[GC_NO_VERIFY_SSL]))
         credentials.refresh(request)
         result = u'PASS'
       except httplib2.ServerNotFoundError as e:
diff --git a/src/google_auth_httplib2.py b/src/google_auth_httplib2/__init__.py
similarity index 91%
rename from src/google_auth_httplib2.py
rename to src/google_auth_httplib2/__init__.py
index c49c136f..51c406eb 100644
--- a/src/google_auth_httplib2.py
+++ b/src/google_auth_httplib2/__init__.py
@@ -80,9 +80,8 @@ class Request(transport.Request):
 
     .. automethod:: __call__
     """
-    def __init__(self, http, user_agent=None):
+    def __init__(self, http):
         self.http = http
-        self.user_agent = user_agent
 
     def __call__(self, url, method='GET', body=None, headers=None,
                  timeout=None, **kwargs):
@@ -112,12 +111,6 @@ class Request(transport.Request):
                 'Set the timeout when constructing the httplib2.Http instance.'
             )
 
-        if self.user_agent:
-          if headers.get('user-agent'):
-            headers['user-agent'] = '%s %s' % (self.user_agent, headers['user-agent'])
-          else:
-            headers['user-agent'] = self.user_agent
-
         try:
             _LOGGER.debug('Making request: %s %s', method, url)
             response, data = self.http.request(
@@ -154,7 +147,7 @@ class AuthorizedHttp(object):
     The underlying :meth:`request` implementation handles adding the
     credentials' headers to the request and refreshing credentials as needed.
     """
-    def __init__(self, credentials, http=None, user_agent=None,
+    def __init__(self, credentials, http=None,
                  refresh_status_codes=transport.DEFAULT_REFRESH_STATUS_CODES,
                  max_refresh_attempts=transport.DEFAULT_MAX_REFRESH_ATTEMPTS):
         """
@@ -164,7 +157,6 @@ class AuthorizedHttp(object):
             http (httplib2.Http): The underlying HTTP object to
                 use to make requests. If not specified, a
                 :class:`httplib2.Http` instance will be constructed.
-            user_agent: the user-agent header
             refresh_status_codes (Sequence[int]): Which HTTP status codes
                 indicate that credentials should be refreshed and the request
                 should be retried.
@@ -177,12 +169,11 @@ class AuthorizedHttp(object):
 
         self.http = http
         self.credentials = credentials
-        self.user_agent = user_agent
         self._refresh_status_codes = refresh_status_codes
         self._max_refresh_attempts = max_refresh_attempts
         # Request instance used by internal methods (for example,
         # credentials.refresh).
-        self._request = Request(self.http, self.user_agent)
+        self._request = Request(self.http)
 
     def request(self, uri, method='GET', body=None, headers=None,
                 **kwargs):
@@ -195,12 +186,6 @@ class AuthorizedHttp(object):
         # and we want to pass the original headers if we recurse.
         request_headers = headers.copy() if headers is not None else {}
 
-        if self.user_agent:
-          if request_headers.get('user-agent'):
-            request_headers['user-agent'] = '%s %s' % (self.user_agent, request_headers['user-agent'])
-          else:
-            request_headers['user-agent'] = self.user_agent
-
         self.credentials.before_request(
             self._request, method, uri, request_headers)