diff --git a/src/calibre/library/catalogs/epub_mobi_builder.py b/src/calibre/library/catalogs/epub_mobi_builder.py
index 2ffe46a6bf..02e4050456 100644
--- a/src/calibre/library/catalogs/epub_mobi_builder.py
+++ b/src/calibre/library/catalogs/epub_mobi_builder.py
@@ -2746,7 +2746,10 @@ class CatalogBuilder(object):
         # Date of publication
         if book['date']:
             pubdate = book['date']
-            pubmonth, pubyear = pubdate.split()
+            try:
+                pubmonth, pubyear = pubdate.split()
+            except Exception:
+                pubmonth = pubyear = ''
         else:
             pubdate = pubyear = pubmonth = ''