diff --git a/beets/autotag/__init__.py b/beets/autotag/__init__.py
index ce3cbde23..4fb9b6f5c 100644
--- a/beets/autotag/__init__.py
+++ b/beets/autotag/__init__.py
@@ -198,7 +198,9 @@ def string_dist(str1, str2):
             # the current case), recalculate the distances for the
             # modified strings.
             case_dist = _string_dist_basic(case_str1, case_str2)
-            case_delta = max(0, base_dist - case_dist)
+            case_delta = max(0.0, base_dist - case_dist)
+            if case_delta == 0.0:
+                continue
             
             # Shift our baseline strings down (to avoid rematching the
             # same part of the string) and add a scaled distance
diff --git a/test/test_autotag.py b/test/test_autotag.py
index 466b84d29..29e950eb0 100644
--- a/test/test_autotag.py
+++ b/test/test_autotag.py
@@ -305,6 +305,10 @@ class StringDistanceTest(unittest.TestCase):
         autotag.string_dist('(EP)', '(EP)')
         autotag.string_dist(', An', '')
 
+    def test_heuristic_does_not_harm_distance(self):
+        dist = autotag.string_dist('Untitled', '[Untitled]')
+        self.assertEqual(dist, 0.0)
+
 def suite():
     return unittest.TestLoader().loadTestsFromName(__name__)