diff --git a/docxcompose/composer.py b/docxcompose/composer.py
index 7b13fae..8ae6245 100644
--- a/docxcompose/composer.py
+++ b/docxcompose/composer.py
@@ -329,7 +329,11 @@ def add_numberings(self, doc, element):
 
         next_num_id, next_anum_id = self._next_numbering_ids()
 
-        src_numbering_part = doc.part.numbering_part
+        # Fixing Issue #68
+        try:
+            src_numbering_part = doc.part.numbering_part
+        except NotImplementedError:
+            return
 
         for num_id in num_ids:
             if num_id in self.num_id_mapping: