diff --git a/mercurial/manifest.py b/mercurial/manifest.py
--- a/mercurial/manifest.py
+++ b/mercurial/manifest.py
@@ -164,7 +164,7 @@ class manifestdict(object):
             return self.copy()
 
         files = match.files()
-        if (match.matchfn == match.exact or
+        if ((match.matchfn == match.exact and len(files) < 100) or
             (not match.anypats() and util.all(fn in self for fn in files))):
             return self.intersectfiles(files)