diff -Nur calibre-4.19.0.orig/src/calibre/utils/config.py calibre-4.19.0/src/calibre/utils/config.py
--- calibre-4.19.0.orig/src/calibre/utils/config.py	2020-07-01 17:51:39.590637064 -0700
+++ calibre-4.19.0/src/calibre/utils/config.py	2020-07-01 17:50:51.287601015 -0700
@@ -363,29 +363,26 @@
         self.update(d)
 
     def __getitem__(self, key):
-        from polyglot.plistlib import Data
         try:
             ans = dict.__getitem__(self, key)
-            if isinstance(ans, Data):
+            if isinstance(ans, bytes):
                 ans = ans.data
             return ans
         except KeyError:
             return self.defaults.get(key, None)
 
     def get(self, key, default=None):
-        from polyglot.plistlib import Data
         try:
             ans = dict.__getitem__(self, key)
-            if isinstance(ans, Data):
+            if isinstance(ans, bytes):
                 ans = ans.data
             return ans
         except KeyError:
             return self.defaults.get(key, default)
 
     def __setitem__(self, key, val):
-        from polyglot.plistlib import Data
         if isinstance(val, bytes):
-            val = Data(val)
+            val = bytes(val)
         dict.__setitem__(self, key, val)
         self.commit()
 
diff -Nur calibre-4.19.0.orig/src/polyglot/plistlib.py calibre-4.19.0/src/polyglot/plistlib.py
--- calibre-4.19.0.orig/src/polyglot/plistlib.py	2020-07-01 17:51:39.601637072 -0700
+++ calibre-4.19.0/src/polyglot/plistlib.py	2020-07-01 17:51:23.458625025 -0700
@@ -6,6 +6,6 @@
 from polyglot.builtins import is_py3
 
 if is_py3:
-    from plistlib import loads, dumps, Data  # noqa
+    from plistlib import loads, dumps # noqa
 else:
     from plistlib import readPlistFromString as loads, writePlistToString as dumps, Data  # noqa