diff --git a/src/applications/diffusion/conduit/DiffusionUpdateCoverageConduitAPIMethod.php b/src/applications/diffusion/conduit/DiffusionUpdateCoverageConduitAPIMethod.php
--- a/src/applications/diffusion/conduit/DiffusionUpdateCoverageConduitAPIMethod.php
+++ b/src/applications/diffusion/conduit/DiffusionUpdateCoverageConduitAPIMethod.php
@@ -37,15 +37,17 @@
   protected function execute(ConduitAPIRequest $request) {
     $viewer = $request->getUser();
 
-    $repository_phid = $request->getValue('repositoryPHID');
+    $repository_identifier = $request->getValue('repositoryPHID');
     $repository = id(new PhabricatorRepositoryQuery())
       ->setViewer($viewer)
-      ->withPHIDs(array($repository_phid))
+      ->withIdentifiers(array($repository_identifier))
       ->executeOne();
 
     if (!$repository) {
       throw new Exception(
-        pht('No repository exists with PHID "%s".', $repository_phid));
+        pht(
+          'No repository exists with identifier "%s".',
+          $repository_identifier));
     }
 
     $commit_name = $request->getValue('commit');
@@ -112,6 +114,114 @@
           $chunk);
       }
     $conn->saveTransaction();
+
+    // Find all the directories we need to update aggregate coverage for.
+    $affected_directories = array();
+    foreach ($coverage as $path => $coverage) {
+      $ancestors = DiffusionPathIDQuery::expandPathToRoot($path);
+
+      // Get rid of the path itself.
+      array_shift($ancestors);
+      foreach ($ancestors as $ancestor) {
+        $affected_directories[$ancestor] = $ancestor;
+      }
+    }
+
+    // Load all the available coverage. This is much easier than trying to
+    // be surgical about it. Note that we're excluding coverage which starts
+    // with "+", since that's aggregate coverage, and we don't want to add
+    // it up twice.
+    $all_coverage = queryfx_all(
+      $conn,
+      'SELECT pathID, coverage FROM %T WHERE commitID = %d
+        AND coverage NOT LIKE %>',
+      $table_name,
+      $commit->getID(),
+      '+');
+    $all_coverage = ipull($all_coverage, 'coverage', 'pathID');
+
+    if ($all_coverage) {
+      $all_covered_paths = queryfx_all(
+        $conn,
+        'SELECT id, path FROM %T WHERE id IN (%Ld)',
+        PhabricatorRepository::TABLE_PATH,
+        array_keys($all_coverage));
+      $all_covered_paths = ipull($all_covered_paths, 'path', 'id');
+    } else {
+      $all_covered_paths = array();
+    }
+
+    $path_coverage = array();
+    foreach ($all_coverage as $path_id => $coverage) {
+      if (!isset($all_covered_paths[$path_id])) {
+        continue;
+      }
+      $path_string = $all_covered_paths[$path_id];
+      $path_coverage[$path_string] = $coverage;
+    }
+
+    $ancestor_coverage = array();
+    foreach ($path_coverage as $path => $coverage) {
+      $ancestors = DiffusionPathIDQuery::expandPathToRoot($path);
+      array_shift($ancestors);
+      foreach ($ancestors as $ancestor) {
+        if (!isset($affected_directories[$ancestor])) {
+          continue;
+        }
+        if (!isset($ancestor_coverage[$ancestor])) {
+          $ancestor_coverage[$ancestor] = '';
+        }
+        $ancestor_coverage[$ancestor] .= $coverage;
+      }
+    }
+
+    $expect = array(
+      'U',
+      'C',
+      'N',
+      'X',
+    );
+
+    foreach ($ancestor_coverage as $path => $aggregate_coverage) {
+      $counts = array();
+      foreach ($expect as $char) {
+        $counts[$char] = substr_count($aggregate_coverage, $char);
+      }
+      // Mark this as aggregate coverage in JSON format.
+      $ancestor_coverage[$path] = '+J'.phutil_json_encode($counts);
+    }
+
+    $ancestor_paths = array_keys($ancestor_coverage);
+    $ancestor_map = id(new DiffusionPathIDQuery($ancestor_paths))
+      ->loadPathIDs();
+
+    $ancestor_sql = array();
+    foreach ($ancestor_coverage as $path => $aggregate_coverage) {
+      if (empty($ancestor_map[$path])) {
+        continue;
+      }
+
+      $path_id = $ancestor_map[$path];
+
+      $sql[] = qsprintf(
+        $conn,
+        '(%d, %d, %d, %s)',
+        $branch->getID(),
+        $path_id,
+        $commit->getID(),
+        $aggregate_coverage);
+    }
+
+    $conn->openTransaction();
+      foreach (PhabricatorLiskDAO::chunkSQL($sql) as $chunk) {
+        queryfx(
+          $conn,
+          'INSERT INTO %T (branchID, pathID, commitID, coverage) VALUES %Q'.
+          ' ON DUPLICATE KEY UPDATE coverage = VALUES(coverage)',
+          $table_name,
+          $chunk);
+      }
+    $conn->saveTransaction();
   }
 
 }