diff --git a/src/calibre/gui2/actions/edit_metadata.py b/src/calibre/gui2/actions/edit_metadata.py
index 64d6f2cbd6..28e2f21d23 100644
--- a/src/calibre/gui2/actions/edit_metadata.py
+++ b/src/calibre/gui2/actions/edit_metadata.py
@@ -418,7 +418,7 @@ class EditMetadataAction(InterfaceAction):
                     db.set_custom(dest_id, dest_value, num=colnum)
               if db.field_metadata[key]['datatype'] in \
                 ('bool', 'int', 'float', 'rating', 'datetime') \
-                and not dest_value:
+                and dest_value is None:
                 db.set_custom(dest_id, src_value, num=colnum)
               if db.field_metadata[key]['datatype'] == 'series' \
                 and not dest_value:
diff --git a/src/calibre/gui2/library/delegates.py b/src/calibre/gui2/library/delegates.py
index b0fdef4c21..a9c71e526b 100644
--- a/src/calibre/gui2/library/delegates.py
+++ b/src/calibre/gui2/library/delegates.py
@@ -310,6 +310,12 @@ class CcNumberDelegate(QStyledItemDelegate): # {{{
             editor.setDecimals(2)
         return editor
 
+    def setModelData(self, editor, model, index):
+        val = editor.value()
+        if val == editor.minimum():
+            val = None
+        model.setData(index, QVariant(val), Qt.EditRole)
+
     def setEditorData(self, editor, index):
         m = index.model()
         val = m.db.data[index.row()][m.custom_columns[m.column_map[index.column()]]['rec_index']]