diff --git a/src/applications/repository/daemon/PhabricatorGitGraphStream.php b/src/applications/repository/daemon/PhabricatorGitGraphStream.php
index 669cf9c105..b175053528 100644
--- a/src/applications/repository/daemon/PhabricatorGitGraphStream.php
+++ b/src/applications/repository/daemon/PhabricatorGitGraphStream.php
@@ -5,6 +5,7 @@ final class PhabricatorGitGraphStream
 
   private $repository;
   private $iterator;
+  private $startCommit;
 
   private $parents        = array();
   private $dates          = array();
@@ -14,6 +15,7 @@ final class PhabricatorGitGraphStream
     $start_commit = null) {
 
     $this->repository = $repository;
+    $this->startCommit = $start_commit;
 
     if ($start_commit !== null) {
       $future = $repository->getLocalCommandFuture(
@@ -82,10 +84,18 @@ final class PhabricatorGitGraphStream
       }
     }
 
-    throw new Exception(
-      pht(
-        "No such commit '%s' in repository!",
-        $commit));
+    if ($this->startCommit !== null) {
+      throw new Exception(
+        pht(
+          'Commit "%s" is not a reachable ancestor of "%s".',
+          $commit,
+          $this->startCommit));
+    } else {
+      throw new Exception(
+        pht(
+          'Commit "%s" is not a reachable ancestor of any ref.',
+          $commit));
+    }
   }
 
   private function isParsed($commit) {
diff --git a/src/applications/repository/engine/PhabricatorRepositoryDiscoveryEngine.php b/src/applications/repository/engine/PhabricatorRepositoryDiscoveryEngine.php
index cdb7e11d03..fd8c57e9b4 100644
--- a/src/applications/repository/engine/PhabricatorRepositoryDiscoveryEngine.php
+++ b/src/applications/repository/engine/PhabricatorRepositoryDiscoveryEngine.php
@@ -157,7 +157,12 @@ final class PhabricatorRepositoryDiscoveryEngine
       $name = $ref->getShortName();
       $commit = $ref->getCommitIdentifier();
 
-      $this->log(pht('Examining ref "%s", at "%s".', $name, $commit));
+      $this->log(
+        pht(
+          'Examining "%s" (%s) at "%s".',
+          $name,
+          $ref->getRefType(),
+          $commit));
 
       if (!$repository->shouldTrackRef($ref)) {
         $this->log(pht('Skipping, ref is untracked.'));
@@ -169,6 +174,15 @@ final class PhabricatorRepositoryDiscoveryEngine
         continue;
       }
 
+      // In Git, it's possible to tag a tag. We just skip these, we'll discover
+      // them when we process the target tag. See T11180.
+      $fields = $ref->getRawFields();
+      $tag_type = idx($fields, '*objecttype');
+      if ($tag_type == 'tag') {
+        $this->log(pht('Skipping, this is a tag of a tag.'));
+        continue;
+      }
+
       $this->log(pht('Looking for new commits.'));
 
       $head_refs = $this->discoverStreamAncestry(