diff --git a/src/calibre/gui2/metadata/single.py b/src/calibre/gui2/metadata/single.py
index b62aa28a68..d818f2db2a 100644
--- a/src/calibre/gui2/metadata/single.py
+++ b/src/calibre/gui2/metadata/single.py
@@ -388,6 +388,10 @@ class MetadataSingleDialogBase(ResizableDialog):
 
     def apply_changes(self):
         self.changed.add(self.book_id)
+        if self.db is None:
+            # break_cycles has already been called, don't know why this should
+            # happen but a user reported it
+            return True
         for widget in self.basic_metadata_widgets:
             try:
                 if not widget.commit(self.db, self.book_id):