diff -r d7c31c73b1bd Lib/csv.py
--- a/Lib/csv.py	Sun Sep 04 12:31:47 2016 +0100
+++ b/Lib/csv.py	Sun Sep 04 22:15:18 2016 +0530
@@ -141,7 +141,7 @@
 
     def writeheader(self):
         header = dict(zip(self.fieldnames, self.fieldnames))
-        self.writerow(header)
+        return self.writerow(header)
 
     def _dict_to_list(self, rowdict):
         if self.extrasaction == "raise":