diff --git a/gerrit_util.py b/gerrit_util.py
index c8d838c7e..984fa1014 100755
--- a/gerrit_util.py
+++ b/gerrit_util.py
@@ -14,6 +14,7 @@ import json
 import logging
 import netrc
 import os
+import re
 import time
 import urllib
 from cStringIO import StringIO
@@ -38,6 +39,10 @@ class GerritError(Exception):
     self.message = '(%d) %s' % (self.http_status, self.message)
 
 
+class GerritAuthenticationError(GerritError):
+  """Exception class for authentication errors during Gerrit communication."""
+
+
 def _QueryString(param_dict, first_param=None):
   """Encodes query parameters in the key:val[+key:val...] format specified here:
 
@@ -115,6 +120,17 @@ def ReadHttpResponse(conn, expect_status=200, ignore_404=True):
   sleep_time = 0.5
   for idx in range(TRY_LIMIT):
     response = conn.getresponse()
+
+    # Check if this is an authentication issue.
+    www_authenticate = response.getheader('www-authenticate')
+    if (response.status in (httplib.UNAUTHORIZED, httplib.FOUND) and
+        www_authenticate):
+      auth_match = re.search('realm="([^"]+)"', www_authenticate, re.I)
+      host = auth_match.group(1) if auth_match else conn.req_host
+      reason = ('Authentication failed. Please make sure your .netrc file '
+                'has credentials for %s' % host)
+      raise GerritAuthenticationError(response.status, reason)
+
     # If response.status < 500 then the result is final; break retry loop.
     if response.status < 500:
       break
diff --git a/trychange.py b/trychange.py
index fc9c1eb1f..7ad2fa126 100755
--- a/trychange.py
+++ b/trychange.py
@@ -779,8 +779,12 @@ def _SendChangeGerrit(bot_spec, options):
 
   change_id = GetChangeId(head_sha)
 
-  # Check that the uploaded revision matches the local one.
-  changes = gerrit_util.GetChangeCurrentRevision(gerrit_host, change_id)
+  try:
+    # Check that the uploaded revision matches the local one.
+    changes = gerrit_util.GetChangeCurrentRevision(gerrit_host, change_id)
+  except gerrit_util.GerritAuthenticationError, e:
+    raise NoTryServerAccess(e.message)
+
   assert len(changes) <= 1, 'Multiple changes with id %s' % change_id
   if not changes:
     raise Error('A change %s was not found on the server. Was it uploaded?' %