diff --git a/src/calibre/ebooks/metadata/opf2.py b/src/calibre/ebooks/metadata/opf2.py
index b83e0f5177..82e5127b59 100644
--- a/src/calibre/ebooks/metadata/opf2.py
+++ b/src/calibre/ebooks/metadata/opf2.py
@@ -460,6 +460,7 @@ def serialize_user_metadata(metadata_elem, all_user_metadata, tail='\n'+(' '*8))
             if fm.get('is_multiple'):
                 # migrate is_multiple back to a character
                 fm = copy.copy(fm)
+                fm['is_multiple2'] = fm.get('is_multiple', {})
                 dt = fm.get('datatype', None)
                 if dt == 'composite':
                     fm['is_multiple'] = ','
@@ -593,17 +594,25 @@ class OPF(object): # {{{
             fm = elem.get('content')
             try:
                 fm = json.loads(fm, object_hook=from_json)
-                im = fm.get('is_multiple', None)
-                if im and not isinstance(im, dict):
-                    # Must migrate the is_multiple from char to dict
-                    dt = fm.get('datatype', None)
-                    if dt == 'composite':
-                        im = {'cache_to_list': ',', 'ui_to_list': ',', 'list_to_ui': ', '}
-                    elif fm.get('display', {}).get('is_names', False):
-                        im = {'cache_to_list': '|', 'ui_to_list': '&', 'list_to_ui': ', '}
-                    else:
-                        im = {'cache_to_list': '|', 'ui_to_list': ',', 'list_to_ui': ', '}
+                im = fm.get('is_multiple2',  None)
+                if im:
                     fm['is_multiple'] = im
+                    del fm['is_multiple2']
+                else:
+                    # Must migrate the is_multiple from char to dict
+                    im = fm.get('is_multiple',  None)
+                    if im:
+                        dt = fm.get('datatype', None)
+                        if dt == 'composite':
+                            im = {'cache_to_list': ',', 'ui_to_list': ',',
+                                  'list_to_ui': ', '}
+                        elif fm.get('display', {}).get('is_names', False):
+                            im = {'cache_to_list': '|', 'ui_to_list': '&',
+                                  'list_to_ui': ', '}
+                        else:
+                            im = {'cache_to_list': '|', 'ui_to_list': ',',
+                                  'list_to_ui': ', '}
+                        fm['is_multiple'] = im
                 temp.set_user_metadata(name, fm)
             except:
                 prints('Failed to read user metadata:', name)