diff --git a/beets/mediafile.py b/beets/mediafile.py
index 3faf2f60e..784695c1a 100644
--- a/beets/mediafile.py
+++ b/beets/mediafile.py
@@ -59,7 +59,7 @@ import enum
 
 from beets import logging
 from beets.util import displayable_path, syspath, as_string
-from beets.util.collections import IdentityUnlessDict
+from beets.util.collections import IdentityFallbackDict
 import six
 
 
@@ -82,7 +82,7 @@ TYPES = {
     'aiff': 'AIFF',
 }
 
-PREFERRED_IMAGE_EXTENSIONS = IdentityUnlessDict({'jpeg': 'jpg'})
+PREFERRED_IMAGE_EXTENSIONS = IdentityFallbackDict({'jpeg': 'jpg'})
 
 
 # Exceptions.
diff --git a/beets/util/collections.py b/beets/util/collections.py
index dad49a4a4..6813b95df 100644
--- a/beets/util/collections.py
+++ b/beets/util/collections.py
@@ -16,7 +16,7 @@
 """
 
 
-class IdentityUnlessDict(dict):
+class IdentityFallbackDict(dict):
     """A dictionary which is "transparent" (maps keys to themselves) for all
     keys not in it.
     """