diff --git a/pytools/persistent_dict.py b/pytools/persistent_dict.py
index 21eb9853470c89a8c022abd5dc088a89a08162b8..c33f2404ebff71a9cc825f38dca0bef678f0227f 100644
--- a/pytools/persistent_dict.py
+++ b/pytools/persistent_dict.py
@@ -28,12 +28,13 @@ THE SOFTWARE.
 
 import logging
 import hashlib
+import collections.abc as abc
 
-try:
-    import collections.abc as abc
-except ImportError:
-    # Python 2
-    import collections as abc
+# Removing this in 2020-12 broke a shocking amount of stuff, such as
+# https://github.com/OP2/PyOP2/pull/605
+# Bring it back for now to mitigate the breakage, however this is going
+# away in 2021 at the latest.
+new_hash = hashlib.sha256
 
 import os
 import shutil