diff --git a/src/calibre/library/save_to_disk.py b/src/calibre/library/save_to_disk.py
index 550ac3251e..a2b8b01a8f 100644
--- a/src/calibre/library/save_to_disk.py
+++ b/src/calibre/library/save_to_disk.py
@@ -20,6 +20,7 @@ from calibre.ebooks.metadata import title_sort
 from calibre.utils.date import parse_date, as_local_time
 from calibre import strftime, prints, sanitize_file_name_unicode
 from calibre.ptempfile import SpooledTemporaryFile
+from calibre.db.lazy import FormatsList
 
 plugboard_any_device_value = 'any device'
 plugboard_any_format_value = 'any format'
@@ -159,7 +160,7 @@ class Formatter(TemplateFormatter):
                 return self.composite_values[key]
             if key in kwargs:
                 val = kwargs[key]
-                if isinstance(val, list):
+                if isinstance(val, list) or isinstance(val, FormatsList):
                     val = ','.join(val)
                 return val.replace('/', '_').replace('\\', '_')
             return ''
diff --git a/src/calibre/utils/formatter.py b/src/calibre/utils/formatter.py
index 89e2395dff..0711013437 100644
--- a/src/calibre/utils/formatter.py
+++ b/src/calibre/utils/formatter.py
@@ -526,6 +526,8 @@ class ValidateFormatter(TemplateFormatter):
         return self._validation_string
 
     def validate(self, x):
+        from calibre.ebooks.metadata.book.base import Metadata
+        self.book = Metadata('');
         return self.vformat(x, [], {})
 
 validation_formatter = ValidateFormatter()