diff --git a/overviewer_core/tileset.py b/overviewer_core/tileset.py
index 7873b89..deae45f 100644
--- a/overviewer_core/tileset.py
+++ b/overviewer_core/tileset.py
@@ -923,8 +923,9 @@ class TileSet(object):
                         raise
                     tile_mtime = 0
 
-                if tile_mtime > max_child_mtime:
-                    # Needs rendering
+                if tile_mtime < max_child_mtime:
+                    # If any child was updated more recently than ourself, then
+                    # we need rendering
                     yield path, None, True
                 else:
                     # Nope.
diff --git a/test/test_tileset.py b/test/test_tileset.py
index 9751726..4abd86f 100644
--- a/test/test_tileset.py
+++ b/test/test_tileset.py
@@ -5,7 +5,6 @@ from collections import defaultdict
 import os
 import os.path
 import random
-import pprint
 
 from overviewer_core import tileset, util
 
@@ -218,11 +217,9 @@ class TilesetTest(unittest.TestCase):
 
         """
         paths = set(x[0] for x in ts.iterate_work_items(0))
-        pprint.pprint(paths)
 
         # Get what tiles we expect to be returned
         expected = get_tile_set(chunks)
-        pprint.pprint(set(expected.iterkeys()))
 
         # Check that all paths returned are in the expected list
         for tilepath in paths:
@@ -289,6 +286,7 @@ class TilesetTest(unittest.TestCase):
         # Strategy: set some tiles on disk to mtime 3, and TileSet needs to
         # find them and update them to mtime 5 as reported by the RegionSet
         # object.
+        # Chosen at random:
         outdated_tiles = [
                 (0,3,3),
                 (1,2,1),
@@ -318,8 +316,6 @@ class TilesetTest(unittest.TestCase):
         # Now see if it's right
         paths = set(x[0] for x in ts.iterate_work_items(0))
         expected = set(outdated_tiles) | set(additional)
-        pprint.pprint(paths)
-        pprint.pprint(expected)
         for tilepath in paths:
             self.assertTrue(tilepath in expected, "%s was not expected to be returned. Expected %s" % (tilepath, expected))