diff --git a/src/calibre/ebooks/metadata/book/render.py b/src/calibre/ebooks/metadata/book/render.py
index 947462ff1d..44ac70bc05 100644
--- a/src/calibre/ebooks/metadata/book/render.py
+++ b/src/calibre/ebooks/metadata/book/render.py
@@ -69,7 +69,7 @@ def mi_to_html(mi, field_list=None, default_author_link=None, use_roman_numbers=
             continue
         if field == 'sort':
             field = 'title_sort'
-        if metadata['datatype'] == 'bool':
+        if metadata['is_custom'] and metadata['datatype'] in {'bool', 'int', 'float'}:
             isnull = mi.get(field) is None
         else:
             isnull = mi.is_null(field)
diff --git a/src/calibre/gui2/custom_column_widgets.py b/src/calibre/gui2/custom_column_widgets.py
index 69de55df61..c8901fe7d8 100644
--- a/src/calibre/gui2/custom_column_widgets.py
+++ b/src/calibre/gui2/custom_column_widgets.py
@@ -20,6 +20,7 @@ from calibre.gui2.dialogs.tag_editor import TagEditor
 from calibre.utils.config import tweaks
 from calibre.utils.icu import sort_key
 from calibre.library.comments import comments_to_html
+from calibre.gui2.library.delegates import ClearingDoubleSpinBox, ClearingSpinBox
 
 class Base(object):
 
@@ -91,7 +92,7 @@ class Int(Base):
 
     def setup_ui(self, parent):
         self.widgets = [QLabel('&'+self.col_metadata['name']+':', parent),
-                QSpinBox(parent)]
+                ClearingSpinBox(parent)]
         w = self.widgets[1]
         w.setRange(-1000000, 100000000)
         w.setSpecialValueText(_('Undefined'))
@@ -114,7 +115,7 @@ class Float(Int):
 
     def setup_ui(self, parent):
         self.widgets = [QLabel('&'+self.col_metadata['name']+':', parent),
-                QDoubleSpinBox(parent)]
+                ClearingDoubleSpinBox(parent)]
         w = self.widgets[1]
         w.setRange(-1000000., float(100000000))
         w.setDecimals(2)