diff --git a/hgext3rd/fbsparse.py b/hgext3rd/fbsparse.py
--- a/hgext3rd/fbsparse.py
+++ b/hgext3rd/fbsparse.py
@@ -1173,18 +1173,31 @@
             _("the current working directory should begin "
               "with the root %s") % root)
 
+    tmf = None
+    if util.safehasattr(mf, '_treemanifest'):
+        # Hybrid manifest, use the (much) faster subtree support
+        tmf = mf._treemanifest()
+
+    if tmf is not None:
+        # a treemanifest is available for this revision
+        matcher = matchmod.match(
+            repo.root, repo.getcwd(),
+            patterns=['path:' + cwd])
+        files = tmf.matches(matcher)
+    else:
+        files = (f for f in mf if f.startswith(cwd))
+
     sparsematch = repo.sparsematch(ctx.rev())
     checkedoutentries = set()
     allentries = set()
     cwdlength = len(cwd)
 
-    for filepath in mf:
-        if filepath.startswith(cwd):
-            entryname = filepath[cwdlength:].partition(os.sep)[0]
+    for filepath in files:
+        entryname = filepath[cwdlength:].partition(os.sep)[0]
 
-            allentries.add(entryname)
-            if sparsematch(filepath):
-                checkedoutentries.add(entryname)
+        allentries.add(entryname)
+        if sparsematch(filepath):
+            checkedoutentries.add(entryname)
 
     ui = repo.ui
     for entry in sorted(allentries):