diff --git a/src/applications/diffusion/conduit/ConduitAPI_diffusion_historyquery_Method.php b/src/applications/diffusion/conduit/ConduitAPI_diffusion_historyquery_Method.php
index d6c6aab39e..3d552d0725 100644
--- a/src/applications/diffusion/conduit/ConduitAPI_diffusion_historyquery_Method.php
+++ b/src/applications/diffusion/conduit/ConduitAPI_diffusion_historyquery_Method.php
@@ -128,6 +128,7 @@ extends ConduitAPI_diffusion_abstractquery_Method {
       hgsprintf('reverse(%s::%s)', '0', $commit_hash),
       $path_arg);
 
+    $stdout = PhabricatorRepository::filterMercurialDebugOutput($stdout);
     $lines = explode("\n", trim($stdout));
     $lines = array_slice($lines, $offset);
 
diff --git a/src/applications/diffusion/query/lowlevel/DiffusionLowLevelMercurialBranchesQuery.php b/src/applications/diffusion/query/lowlevel/DiffusionLowLevelMercurialBranchesQuery.php
index cd1cbcd720..602b2b6123 100644
--- a/src/applications/diffusion/query/lowlevel/DiffusionLowLevelMercurialBranchesQuery.php
+++ b/src/applications/diffusion/query/lowlevel/DiffusionLowLevelMercurialBranchesQuery.php
@@ -12,6 +12,7 @@ final class DiffusionLowLevelMercurialBranchesQuery
     // NOTE: `--debug` gives us 40-character hashes.
     list($stdout) = $repository->execxLocalCommand(
       '--debug branches');
+    $stdout = PhabricatorRepository::filterMercurialDebugOutput($stdout);
 
     $branches = array();
 
diff --git a/src/applications/diffusion/query/parents/DiffusionMercurialCommitParentsQuery.php b/src/applications/diffusion/query/parents/DiffusionMercurialCommitParentsQuery.php
index ec19f9cbce..dc9f900ce8 100644
--- a/src/applications/diffusion/query/parents/DiffusionMercurialCommitParentsQuery.php
+++ b/src/applications/diffusion/query/parents/DiffusionMercurialCommitParentsQuery.php
@@ -10,6 +10,7 @@ final class DiffusionMercurialCommitParentsQuery
     list($stdout) = $repository->execxLocalCommand(
       'log --debug --limit 1 --template={parents} --rev %s',
       $drequest->getStableCommitName());
+    $stdout = PhabricatorRepository::filterMercurialDebugOutput($stdout);
 
     $hashes = preg_split('/\s+/', trim($stdout));
     foreach ($hashes as $key => $value) {
diff --git a/src/applications/repository/storage/PhabricatorRepository.php b/src/applications/repository/storage/PhabricatorRepository.php
index 2ce03840a0..64ce761e72 100644
--- a/src/applications/repository/storage/PhabricatorRepository.php
+++ b/src/applications/repository/storage/PhabricatorRepository.php
@@ -440,6 +440,29 @@ final class PhabricatorRepository extends PhabricatorRepositoryDAO
     return $args;
   }
 
+  /**
+   * 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
+
+    $lines = preg_split('/(?<=\n)/', $stdout);
+    $regex = '/ignoring untrusted configuration option .*\n$/';
+
+    foreach ($lines as $key => $line) {
+      $lines[$key] = preg_replace($regex, '', $line);
+    }
+
+    return implode('', $lines);
+  }
+
   public function getURI() {
     return '/diffusion/'.$this->getCallsign().'/';
   }
diff --git a/src/applications/repository/storage/__tests__/PhabricatorRepositoryTestCase.php b/src/applications/repository/storage/__tests__/PhabricatorRepositoryTestCase.php
index 69f18f454a..5b60b2968e 100644
--- a/src/applications/repository/storage/__tests__/PhabricatorRepositoryTestCase.php
+++ b/src/applications/repository/storage/__tests__/PhabricatorRepositoryTestCase.php
@@ -107,5 +107,52 @@ final class PhabricatorRepositoryTestCase
 
   }
 
+  public function testFilterMercurialDebugOutput() {
+    $map = array(
+      "" => "",
+
+      "quack\n" => "quack\n",
+
+      "ignoring untrusted configuration option x.y = z\nquack\n" =>
+        "quack\n",
+
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "quack\n" =>
+        "quack\n",
+
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "quack\n" =>
+        "quack\n",
+
+      "quack\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n" =>
+        "quack\n",
+
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "duck\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "bread\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "quack\n" =>
+        "duck\nbread\nquack\n",
+
+      "ignoring untrusted configuration option x.y = z\n".
+      "duckignoring untrusted configuration option x.y = z\n".
+      "quack" =>
+        "duckquack",
+    );
+
+    foreach ($map as $input => $expect) {
+      $actual = PhabricatorRepository::filterMercurialDebugOutput($input);
+      $this->assertEqual($expect, $actual, $input);
+    }
+  }
 
 }