diff --git a/src/calibre/db/fields.py b/src/calibre/db/fields.py
index ac96cb837d..9becf82403 100644
--- a/src/calibre/db/fields.py
+++ b/src/calibre/db/fields.py
@@ -163,12 +163,13 @@ class CompositeField(OneToOneField):
 
         self._render_cache = {}
         self._lock = Lock()
+        self._composite_name = '#' + self.metadata['label']
 
     def render_composite(self, book_id, mi):
         with self._lock:
             ans = self._render_cache.get(book_id, None)
         if ans is None:
-            ans = mi.get('#'+self.metadata['label'])
+            ans = mi.get(self._composite_name)
             with self._lock:
                 self._render_cache[book_id] = ans
         return ans
@@ -186,7 +187,7 @@ class CompositeField(OneToOneField):
             ans = self._render_cache.get(book_id, None)
         if ans is None:
             mi = get_metadata(book_id)
-            ans = mi.get('#'+self.metadata['label'])
+            ans = mi.get(self._composite_name)
             with self._lock:
                 self._render_cache[book_id] = ans
         return ans
diff --git a/src/calibre/db/tests/profiling.py b/src/calibre/db/tests/profiling.py
index 6cff57f990..07365b1b75 100644
--- a/src/calibre/db/tests/profiling.py
+++ b/src/calibre/db/tests/profiling.py
@@ -25,8 +25,12 @@ def show_stats(path):
 def main():
     stats = os.path.join(gettempdir(), 'read_db.stats')
     pr = cProfile.Profile()
+    initdb('~/test library')
+    all_ids = db.new_api.all_book_ids()  # noqa
     pr.enable()
-    initdb('~/documents/largelib')
+    for book_id in all_ids:
+        db.new_api._composite_for('#isbn', book_id)
+        db.new_api._composite_for('#formats', book_id)
     pr.disable()
     pr.dump_stats(stats)
     show_stats(stats)