diff --git a/apiclient/discovery.py b/apiclient/discovery.py
index 5ae7f02..1bac08c 100644
--- a/apiclient/discovery.py
+++ b/apiclient/discovery.py
@@ -64,6 +64,11 @@
   def request(self, headers, path_params, query_params, body_value):
     query = self.build_query(query_params)
     headers['accept'] = 'application/json'
+    if 'user-agent' in headers:
+      headers['user-agent'] += ' '
+    else:
+      headers['user-agent'] = ''
+    headers['user-agent'] += 'google-api-client-python/1.0'
     if body_value is None:
       return (headers, path_params, query, None)
     else: