diff --git a/Lib/email/generator.py b/Lib/email/generator.py
--- a/Lib/email/generator.py
+++ b/Lib/email/generator.py
@@ -297,10 +297,12 @@
         # message/rfc822.  Such messages are generated by, for example,
         # Groupwise when forwarding unadorned messages.  (Issue 7970.)  So
         # in that case we just emit the string body.
-        payload = msg.get_payload()
+        payload = msg._payload
         if isinstance(payload, list):
             g.flatten(msg.get_payload(0), unixfrom=False, linesep=self._NL)
             payload = s.getvalue()
+        else:
+            payload = self._encode(payload)
         self._fp.write(payload)
 
     # This used to be a module level function; we use a classmethod for this