diff --git a/src/calibre/library/custom_columns.py b/src/calibre/library/custom_columns.py
index e039f5a817..5b459c6d2a 100644
--- a/src/calibre/library/custom_columns.py
+++ b/src/calibre/library/custom_columns.py
@@ -12,6 +12,7 @@ from math import floor
 
 from calibre import prints
 from calibre.constants import preferred_encoding
+from calibre.library.field_metadata import FieldMetadata
 from calibre.utils.date import parse_date
 
 class CustomColumns(object):
@@ -30,6 +31,10 @@ class CustomColumns(object):
 
 
     def __init__(self):
+        # Verify that CUSTOM_DATA_TYPES is a (possibly improper) subset of
+        # VALID_DATA_TYPES
+        if len(self.CUSTOM_DATA_TYPES - FieldMetadata.VALID_DATA_TYPES) > 0:
+            raise ValueError('Unknown custom column type in set')
         # Delete marked custom columns
         for record in self.conn.get(
                 'SELECT id FROM custom_columns WHERE mark_for_delete=1'):
diff --git a/src/calibre/library/field_metadata.py b/src/calibre/library/field_metadata.py
index 626683fee5..f29b432eec 100644
--- a/src/calibre/library/field_metadata.py
+++ b/src/calibre/library/field_metadata.py
@@ -30,8 +30,8 @@ class FieldMetadata(dict):
 
     label: the actual column label. No prefixing.
 
-    datatype: the type of the information in the field. Valid values are float,
-    int, rating, bool, comments, datetime, text.
+    datatype: the type of information in the field. Valid values are listed in
+    VALID_DATA_TYPES below.
     is_multiple: valid for the text datatype. If None, the field is to be
     treated as a single term. If not None, it contains a string, and the field
     is assumed to contain a list of terms separated by that string
@@ -65,6 +65,10 @@ class FieldMetadata(dict):
     rec_index: the index of the field in the db metadata record.
 
     '''
+
+    VALID_DATA_TYPES = frozenset([None, 'rating', 'text', 'comments', 'datetime',
+                                  'int', 'float', 'bool', 'series'])
+
     _field_metadata = [
             ('authors',   {'table':'authors',
                            'column':'name',
@@ -296,6 +300,8 @@ class FieldMetadata(dict):
         self._search_term_map = {}
         self.custom_label_to_key_map = {}
         for k,v in self._field_metadata:
+            if v['kind'] == 'field' and v['datatype'] not in self.VALID_DATA_TYPES:
+                raise ValueError('Unknown datatype %s for field %s'%(v['datatype'], k))
             self._tb_cats[k] = v
             self._tb_cats[k]['label'] = k
             self._tb_cats[k]['display'] = {}
@@ -377,6 +383,8 @@ class FieldMetadata(dict):
         key = self.custom_field_prefix + label
         if key in self._tb_cats:
             raise ValueError('Duplicate custom field [%s]'%(label))
+        if datatype not in self.VALID_DATA_TYPES:
+            raise ValueError('Unknown datatype %s for field %s'%(datatype, key))
         self._tb_cats[key] = {'table':table,       'column':column,
                              'datatype':datatype,  'is_multiple':is_multiple,
                              'kind':'field',       'name':name,