diff --git a/src/calibre/ebooks/epub/output.py b/src/calibre/ebooks/epub/output.py
index fd96bfdb94..129a63ef3c 100644
--- a/src/calibre/ebooks/epub/output.py
+++ b/src/calibre/ebooks/epub/output.py
@@ -171,6 +171,10 @@ class EPUBOutput(OutputFormatPlugin):
 
         self.workaround_sony_quirks()
 
+        if self.oeb.toc.count() == 0:
+            self.log.warn('This EPUB file has no Table of Contents. It will '
+                    'not validate via epubcheck')
+
         from calibre.ebooks.oeb.base import OPF
         identifiers = oeb.metadata['identifier']
         uuid = None