diff --git a/locale/en/LC_MESSAGES/django.po b/locale/en/LC_MESSAGES/django.po
index 99e296529d..40fa1df9e8 100644
--- a/locale/en/LC_MESSAGES/django.po
+++ b/locale/en/LC_MESSAGES/django.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2016-03-21 11:17+0800\n"
+"POT-Creation-Date: 2016-03-21 12:21+0800\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -18,10 +18,6 @@ msgstr ""
 "Content-Transfer-Encoding: 8bit\n"
 
 #: seahub/api2/endpoints/group_members.py:91
-#, python-format
-msgid "User %s is already group member."
-msgstr ""
-
 #: seahub/api2/endpoints/group_members.py:279 seahub/views/ajax.py:2518
 #, python-format
 msgid "User %s is already a group member."
diff --git a/locale/en/LC_MESSAGES/djangojs.po b/locale/en/LC_MESSAGES/djangojs.po
index 84cf62593d..d5d07425ea 100644
--- a/locale/en/LC_MESSAGES/djangojs.po
+++ b/locale/en/LC_MESSAGES/djangojs.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2016-03-21 11:17+0800\n"
+"POT-Creation-Date: 2016-03-21 12:21+0800\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
diff --git a/seahub/api2/endpoints/group_members.py b/seahub/api2/endpoints/group_members.py
index 1348dd3b54..5e2560945e 100644
--- a/seahub/api2/endpoints/group_members.py
+++ b/seahub/api2/endpoints/group_members.py
@@ -88,7 +88,7 @@ class GroupMembers(APIView):
                 return api_error(status.HTTP_403_FORBIDDEN, error_msg)
 
             if is_group_member(group_id, email):
-                error_msg = _(u'User %s is already group member.') % email
+                error_msg = _(u'User %s is already a group member.') % email
                 return api_error(status.HTTP_400_BAD_REQUEST, error_msg)
 
             seaserv.ccnet_threaded_rpc.group_add_member(group_id, username, email)