diff --git a/src/applications/diffusion/protocol/DiffusionMercurialCommandEngine.php b/src/applications/diffusion/protocol/DiffusionMercurialCommandEngine.php
index 39d89e3e4c..03705ad49d 100644
--- a/src/applications/diffusion/protocol/DiffusionMercurialCommandEngine.php
+++ b/src/applications/diffusion/protocol/DiffusionMercurialCommandEngine.php
@@ -1,93 +1,98 @@
 <?php
 
 final class DiffusionMercurialCommandEngine
   extends DiffusionCommandEngine {
 
   protected function canBuildForRepository(
     PhabricatorRepository $repository) {
     return $repository->isHg();
   }
 
   protected function newFormattedCommand($pattern, array $argv) {
     $args = array();
 
     // Crudely blacklist commands which look like they may contain command
     // injection via "--config" or "--debugger". See T13012. To do this, we
     // print the whole command, parse it using shell rules, then examine each
     // argument to see if it looks like "--config" or "--debugger".
 
     $test_command = call_user_func_array(
       'csprintf',
       array_merge(array($pattern), $argv));
     $test_args = id(new PhutilShellLexer())
       ->splitArguments($test_command);
 
     foreach ($test_args as $test_arg) {
       if (preg_match('/^--(config|debugger)/i', $test_arg)) {
         throw new DiffusionMercurialFlagInjectionException(
           pht(
             'Mercurial command appears to contain unsafe injected "--config" '.
             'or "--debugger": %s',
             $test_command));
       }
     }
 
     // NOTE: Here, and in Git and Subversion, we override the SSH command even
     // if the repository does not use an SSH remote, since our SSH wrapper
     // defuses an attack against older versions of Mercurial, Git and
     // Subversion (see T12961) and it's possible to execute this attack
     // in indirect ways, like by using an SSH subrepo inside an HTTP repo.
 
     $pattern = "hg --config ui.ssh=%s {$pattern}";
     $args[] = $this->getSSHWrapper();
 
     return array($pattern, array_merge($args, $argv));
   }
 
   protected function newCustomEnvironment() {
     $env = array();
 
     // NOTE: This overrides certain configuration, extensions, and settings
     // which make Mercurial commands do random unusual things.
     $env['HGPLAIN'] = 1;
 
     return $env;
   }
 
   /**
    * Sanitize output of an `hg` command invoked with the `--debug` flag to make
    * it usable.
    *
    * @param string Output from `hg --debug ...`
    * @return string Usable output.
    */
   public static function filterMercurialDebugOutput($stdout) {
     // When hg commands are run with `--debug` and some config file isn't
     // trusted, Mercurial prints out a warning to stdout, twice, after Feb 2011.
     //
     // http://selenic.com/pipermail/mercurial-devel/2011-February/028541.html
     //
     // After Jan 2015, it may also fail to write to a revision branch cache.
+    //
+    // Separately, it may fail to write to a different branch cache, and may
+    // encounter issues reading the branch cache.
 
     $ignore = array(
       'ignoring untrusted configuration option',
       "couldn't write revision branch cache:",
+      "couldn't write branch cache:",
+      'invalid branchheads cache',
     );
 
     foreach ($ignore as $key => $pattern) {
       $ignore[$key] = preg_quote($pattern, '/');
     }
 
     $ignore = '('.implode('|', $ignore).')';
 
     $lines = preg_split('/(?<=\n)/', $stdout);
     $regex = '/'.$ignore.'.*\n$/';
 
     foreach ($lines as $key => $line) {
       $lines[$key] = preg_replace($regex, '', $line);
     }
 
     return implode('', $lines);
   }
 
 }