diff --git a/src/applications/diffusion/conduit/DiffusionLastModifiedQueryConduitAPIMethod.php b/src/applications/diffusion/conduit/DiffusionLastModifiedQueryConduitAPIMethod.php
index 30b436cfff..1135420a6e 100644
--- a/src/applications/diffusion/conduit/DiffusionLastModifiedQueryConduitAPIMethod.php
+++ b/src/applications/diffusion/conduit/DiffusionLastModifiedQueryConduitAPIMethod.php
@@ -115,6 +115,10 @@ final class DiffusionLastModifiedQueryConduitAPIMethod
     $graph_cache = new PhabricatorRepositoryGraphCache();
 
     $results = array();
+
+    // Spend no more than this many total seconds trying to satisfy queries
+    // via the graph cache.
+    $remaining_time = 10.0;
     foreach ($map as $path => $commit) {
       $path_id = idx($path_map, $path);
       if (!$path_id) {
@@ -125,13 +129,21 @@ final class DiffusionLastModifiedQueryConduitAPIMethod
         continue;
       }
 
+      $t_start = microtime(true);
       $cache_result = $graph_cache->loadLastModifiedCommitID(
         $commit_id,
-        $path_id);
+        $path_id,
+        $remaining_time);
+      $t_end = microtime(true);
 
       if ($cache_result !== false) {
         $results[$path] = $cache_result;
       }
+
+      $remaining_time -= ($t_end - $t_start);
+      if ($remaining_time <= 0) {
+        break;
+      }
     }
 
     if ($results) {
diff --git a/src/applications/repository/graphcache/PhabricatorRepositoryGraphCache.php b/src/applications/repository/graphcache/PhabricatorRepositoryGraphCache.php
index d52182fcc9..c4adc61ab0 100644
--- a/src/applications/repository/graphcache/PhabricatorRepositoryGraphCache.php
+++ b/src/applications/repository/graphcache/PhabricatorRepositoryGraphCache.php
@@ -102,6 +102,10 @@ final class PhabricatorRepositoryGraphCache extends Phobject {
         }
 
         // Otherwise, the rebuild gave us the data, so we can keep going.
+
+        $did_fill = true;
+      } else {
+        $did_fill = false;
       }
 
       // Sanity check so we can survive and recover from bad data.
@@ -147,12 +151,17 @@ final class PhabricatorRepositoryGraphCache extends Phobject {
         $commit_id = $parent_id;
 
         // Periodically check if we've spent too long looking for a result
-        // in the cache, and return so we can fall back to a VCS operation. This
-        // keeps us from having a degenerate worst case if, e.g., the cache
-        // is cold and we need to inspect a very large number of blocks
+        // in the cache, and return so we can fall back to a VCS operation.
+        // This keeps us from having a degenerate worst case if, e.g., the
+        // cache is cold and we need to inspect a very large number of blocks
         // to satisfy the query.
 
-        if (((++$iterations) % 64) === 0) {
+        ++$iterations;
+
+        // If we performed a cache fill in this cycle, always check the time
+        // limit, since cache fills may take a significant amount of time.
+
+        if ($did_fill || ($iterations % 64 === 0)) {
           $t_end = microtime(true);
           if (($t_end - $t_start) > $time) {
             return false;