diff --git a/src/calibre/gui2/tag_view.py b/src/calibre/gui2/tag_view.py
index 8d42e51dfc..beedad4757 100644
--- a/src/calibre/gui2/tag_view.py
+++ b/src/calibre/gui2/tag_view.py
@@ -779,8 +779,11 @@ class TagsModel(QAbstractItemModel): # {{{
                                      category_icon = category_node.icon,
                                      category_key=category_node.category_key)
                     else:
-                        if upper(tag.sort[0]) != collapse_letter:
-                            collapse_letter = upper(tag.sort[0])
+                        ts = tag.sort
+                        if not ts:
+                            ts = 'Z'
+                        if upper(ts[0]) != collapse_letter:
+                            collapse_letter = upper(ts[0])
                             sub_cat = TagTreeItem(parent=category,
                                      data = collapse_letter,
                                      category_icon = category_node.icon,