diff --git a/feedgen/entry.py b/feedgen/entry.py
index 71d295a..f7a13a8 100644
--- a/feedgen/entry.py
+++ b/feedgen/entry.py
@@ -668,7 +668,7 @@ def enclosure(self, url=None, length=None, type=None):
         :returns: Data of the enclosure element.
         '''
         if url is not None:
-            self.link(href=url, rel='enclosure', type=type, length=length)
+            self.link(href=url, rel='enclosure', type=type, length=str(length))
         return self.__rss_enclosure
 
     def ttl(self, ttl=None):