diff --git a/pytools/persistent_dict.py b/pytools/persistent_dict.py
index c10d4e9f51d035fcaaafb496d128f2db46e2cbc5..9bc9438f398467592df6d26362cabb8a7453efae 100644
--- a/pytools/persistent_dict.py
+++ b/pytools/persistent_dict.py
@@ -375,6 +375,8 @@ class PersistentDict(object):
                             "indicative of a broken implementation "
                             "of equality comparison"
                             % (self.identifier, self.container_dir))
+                    # This is here so we can debug the equality comparison
+                    read_key == key
                     raise NoSuchEntryError(key)
 
                 logger.debug("%s: cache hit [key=%s]" % (