diff --git a/src/calibre/gui2/viewer/convert_book.py b/src/calibre/gui2/viewer/convert_book.py
index a1f75479f9..52c10fb38c 100644
--- a/src/calibre/gui2/viewer/convert_book.py
+++ b/src/calibre/gui2/viewer/convert_book.py
@@ -118,14 +118,16 @@ def expire_cache_and_temp(temp_path, finished_path, metadata, max_age, force_exp
     for keys in path_key_map.values():
         instances = []
         for key in keys:
-            instances += entries[key]
+            instances += entries.get(key, [])
         if len(instances) > 1:
             removed = tuple(expire_old_versions(finished_path, instances))
             if removed:
                 for r in removed:
-                    entries[r['key']].remove(r)
-                    if not entries[r['key']]:
-                        del entries[r['key']]
+                    rkey = r['key']
+                    if rkey in entries:
+                        entries[rkey].remove(r)
+                        if not entries[rkey]:
+                            del entries[rkey]
     metadata['last_clear_at'] = now