diff --git a/Lib/email/message.py b/Lib/email/message.py
--- a/Lib/email/message.py
+++ b/Lib/email/message.py
@@ -241,7 +241,7 @@
         if i is not None and not isinstance(self._payload, list):
             raise TypeError('Expected list, got %s' % type(self._payload))
         payload = self._payload
-        cte = self.get('content-transfer-encoding', '').lower()
+        cte = str(self.get('content-transfer-encoding', '')).lower()
         # payload can be bytes here, (I wonder if that is actually a bug?)
         if isinstance(payload, str):
             if _has_surrogates(payload):
@@ -562,7 +562,7 @@
         if value is missing:
             return failobj
         params = []
-        for p in _parseparam(';' + value):
+        for p in _parseparam(';' + str(value)):
             try:
                 name, val = p.split('=', 1)
                 name = name.strip()