diff --git a/src/calibre/library/cli.py b/src/calibre/library/cli.py
index 2a3e58f99b..d5eea9696e 100644
--- a/src/calibre/library/cli.py
+++ b/src/calibre/library/cli.py
@@ -42,7 +42,7 @@ def do_list(db, fields, sort_by, ascending, search_text):
     widths = list(map(lambda x : 0, fields))
     for i in db.data:
         for j, field in enumerate(fields):
-            widths[j] = max(widths[j], len(unicode(i[field])))
+            widths[j] = max(widths[j], len(unicode(i[str(field)])))
     
     screen_width = terminal_controller.COLS
     if not screen_width: