diff --git a/src/applications/diffusion/conduit/DiffusionBranchQueryConduitAPIMethod.php b/src/applications/diffusion/conduit/DiffusionBranchQueryConduitAPIMethod.php
index d42c45a96b..62878c0291 100644
--- a/src/applications/diffusion/conduit/DiffusionBranchQueryConduitAPIMethod.php
+++ b/src/applications/diffusion/conduit/DiffusionBranchQueryConduitAPIMethod.php
@@ -1,128 +1,141 @@
 <?php
 
 final class DiffusionBranchQueryConduitAPIMethod
   extends DiffusionQueryConduitAPIMethod {
 
   public function getAPIMethodName() {
     return 'diffusion.branchquery';
   }
 
   public function getMethodDescription() {
     return pht('Determine what branches exist for a repository.');
   }
 
   protected function defineReturnType() {
     return 'list<dict>';
   }
 
   protected function defineCustomParamTypes() {
     return array(
       'closed' => 'optional bool',
       'limit' => 'optional int',
       'offset' => 'optional int',
       'contains' => 'optional string',
     );
   }
 
   protected function getGitResult(ConduitAPIRequest $request) {
     $drequest = $this->getDiffusionRequest();
     $repository = $drequest->getRepository();
 
     $contains = $request->getValue('contains');
     if (strlen($contains)) {
+
+      // See PHI720. If the standard "branch" field is provided, use it
+      // as the "pattern" argument to "git branch ..." to let callers test
+      // for reachability from a particular branch head.
+      $pattern = $request->getValue('branch');
+      if (strlen($pattern)) {
+        $pattern_argv = array($pattern);
+      } else {
+        $pattern_argv = array();
+      }
+
       // NOTE: We can't use DiffusionLowLevelGitRefQuery here because
       // `git for-each-ref` does not support `--contains`.
       if ($repository->isWorkingCopyBare()) {
         list($stdout) = $repository->execxLocalCommand(
-          'branch --verbose --no-abbrev --contains %s --',
-          $contains);
+          'branch --verbose --no-abbrev --contains %s -- %Ls',
+          $contains,
+          $pattern_argv);
         $ref_map = DiffusionGitBranch::parseLocalBranchOutput(
           $stdout);
       } else {
         list($stdout) = $repository->execxLocalCommand(
-          'branch -r --verbose --no-abbrev --contains %s --',
-          $contains);
+          'branch -r --verbose --no-abbrev --contains %s -- %Ls',
+          $contains,
+          $pattern_argv);
         $ref_map = DiffusionGitBranch::parseRemoteBranchOutput(
           $stdout,
           DiffusionGitBranch::DEFAULT_GIT_REMOTE);
       }
 
       $refs = array();
       foreach ($ref_map as $ref => $commit) {
         $refs[] = id(new DiffusionRepositoryRef())
           ->setShortName($ref)
           ->setCommitIdentifier($commit);
       }
     } else {
       $refs = id(new DiffusionLowLevelGitRefQuery())
         ->setRepository($repository)
         ->withRefTypes(
           array(
             PhabricatorRepositoryRefCursor::TYPE_BRANCH,
           ))
         ->execute();
     }
 
     return $this->processBranchRefs($request, $refs);
   }
 
   protected function getMercurialResult(ConduitAPIRequest $request) {
     $drequest = $this->getDiffusionRequest();
     $repository = $drequest->getRepository();
 
     $query = id(new DiffusionLowLevelMercurialBranchesQuery())
       ->setRepository($repository);
 
     $contains = $request->getValue('contains');
     if (strlen($contains)) {
       $query->withContainsCommit($contains);
     }
 
     $refs = $query->execute();
 
     return $this->processBranchRefs($request, $refs);
   }
 
   protected function getSVNResult(ConduitAPIRequest $request) {
     // Since SVN doesn't have meaningful branches, just return nothing for all
     // queries.
     return array();
   }
 
   private function processBranchRefs(ConduitAPIRequest $request, array $refs) {
     $drequest = $this->getDiffusionRequest();
     $repository = $drequest->getRepository();
     $offset = $request->getValue('offset');
     $limit = $request->getValue('limit');
 
     foreach ($refs as $key => $ref) {
       if (!$repository->shouldTrackBranch($ref->getShortName())) {
         unset($refs[$key]);
       }
     }
 
     $with_closed = $request->getValue('closed');
     if ($with_closed !== null) {
       foreach ($refs as $key => $ref) {
         $fields = $ref->getRawFields();
         if (idx($fields, 'closed') != $with_closed) {
           unset($refs[$key]);
         }
       }
     }
 
     // NOTE: We can't apply the offset or limit until here, because we may have
     // filtered untrackable branches out of the result set.
 
     if ($offset) {
       $refs = array_slice($refs, $offset);
     }
 
     if ($limit) {
       $refs = array_slice($refs, 0, $limit);
     }
 
     return mpull($refs, 'toDictionary');
   }
 
 }
diff --git a/src/applications/diffusion/controller/DiffusionCommitBranchesController.php b/src/applications/diffusion/controller/DiffusionCommitBranchesController.php
index e698ff6fc7..633c3b9174 100644
--- a/src/applications/diffusion/controller/DiffusionCommitBranchesController.php
+++ b/src/applications/diffusion/controller/DiffusionCommitBranchesController.php
@@ -1,59 +1,60 @@
 <?php
 
 final class DiffusionCommitBranchesController extends DiffusionController {
 
   public function shouldAllowPublic() {
     return true;
   }
 
   public function handleRequest(AphrontRequest $request) {
     $response = $this->loadDiffusionContext();
     if ($response) {
       return $response;
     }
 
     $drequest = $this->getDiffusionRequest();
     $repository = $drequest->getRepository();
 
     $branch_limit = 10;
     $branches = DiffusionRepositoryRef::loadAllFromDictionaries(
       $this->callConduitWithDiffusionRequest(
         'diffusion.branchquery',
         array(
           'contains' => $drequest->getCommit(),
           'limit' => $branch_limit + 1,
+          'branch' => null,
         )));
 
     $has_more_branches = (count($branches) > $branch_limit);
     $branches = array_slice($branches, 0, $branch_limit);
 
     $branch_links = array();
     foreach ($branches as $branch) {
       $branch_links[] = phutil_tag(
         'a',
         array(
           'href' => $drequest->generateURI(
             array(
               'action'  => 'browse',
               'branch'  => $branch->getShortName(),
             )),
         ),
         $branch->getShortName());
     }
 
     if ($has_more_branches) {
       $branch_links[] = phutil_tag(
         'a',
         array(
           'href' => $drequest->generateURI(
             array(
               'action'  => 'branches',
             )),
         ),
         pht("More Branches\xE2\x80\xA6"));
     }
 
     return id(new AphrontAjaxResponse())
       ->setContent($branch_links ? implode(', ', $branch_links) : pht('None'));
   }
 }