diff --git a/src/calibre/gui2/device.py b/src/calibre/gui2/device.py
index 9ed18d5a84..6c1fa0c4fb 100644
--- a/src/calibre/gui2/device.py
+++ b/src/calibre/gui2/device.py
@@ -1771,7 +1771,10 @@ class DeviceMixin(object):  # {{{
         string_pat = re.compile(r'(?u)\W|[_]')
 
         def clean_string(x):
-            x = x.lower() if x else ''
+            try:
+                x = x.lower() if x else ''
+            except Exception:
+                x = ''
             return string_pat.sub('', x)
 
         update_metadata = (