diff --git a/owners.py b/owners.py
index 407567b866..c117807868 100644
--- a/owners.py
+++ b/owners.py
@@ -418,19 +418,28 @@ class Database(object):
     dirs_remaining = set(self._enclosing_dir_with_owners(f) for f in files)
     all_possible_owners = self.all_possible_owners(dirs_remaining, author)
     suggested_owners = set()
-    if len(all_possible_owners) == 0:
-      return suggested_owners
-    while dirs_remaining:
+    while dirs_remaining and all_possible_owners:
       owner = self.lowest_cost_owner(all_possible_owners, dirs_remaining)
       suggested_owners.add(owner)
       dirs_to_remove = set(el[0] for el in all_possible_owners[owner])
       dirs_remaining -= dirs_to_remove
+      # Now that we've used `owner` and covered all their dirs, remove them
+      # from consideration.
+      del all_possible_owners[owner]
+      for o, dirs in all_possible_owners.items():
+        new_dirs = [(d, dist) for (d, dist) in dirs if d not in dirs_to_remove]
+        if not new_dirs:
+          del all_possible_owners[o]
+        else:
+          all_possible_owners[o] = new_dirs
     return suggested_owners
 
   def all_possible_owners(self, dirs, author):
-    """Returns a list of (potential owner, distance-from-dir) tuples; a
-    distance of 1 is the lowest/closest possible distance (which makes the
-    subsequent math easier)."""
+    """Returns a dict of {potential owner: (dir, distance)} mappings.
+
+    A distance of 1 is the lowest/closest possible distance (which makes the
+    subsequent math easier).
+    """
     all_possible_owners = {}
     for current_dir in dirs:
       dirname = current_dir
diff --git a/tests/owners_unittest.py b/tests/owners_unittest.py
index 0cb0a1ede3..b72a9b6cb1 100755
--- a/tests/owners_unittest.py
+++ b/tests/owners_unittest.py
@@ -467,6 +467,13 @@ class ReviewersForTest(_BaseTestCase):
     self.assert_reviewers_for(['chrome/gpu/gpu_channel.h'],
                               [[ben], [brett]], author=ken)
 
+
+  def test_reviewers_for__ignores_unowned_files(self):
+    # Clear the root OWNERS file.
+    self.files['/OWNERS'] = ''
+    self.assert_reviewers_for(['base/vlog.h', 'chrome/browser/deafults/h'],
+                              [[brett]])
+
   def test_reviewers_file_includes__absolute(self):
     self.assert_reviewers_for(['content/qux/foo.cc'],
                               [[peter], [brett], [john], [darin]])