diff -r b0087e17cd5e Lib/email/mime/text.py
--- a/Lib/email/mime/text.py	Fri Jul 01 17:57:30 2016 +0300
+++ b/Lib/email/mime/text.py	Sat Jul 02 23:24:17 2016 +0200
@@ -35,10 +35,8 @@
                 _charset = 'us-ascii'
             except UnicodeEncodeError:
                 _charset = 'utf-8'
-        if isinstance(_charset, Charset):
-            _charset = str(_charset)
 
         MIMENonMultipart.__init__(self, 'text', _subtype,
-                                  **{'charset': _charset})
+                                  **{'charset': str(_charset)})
 
         self.set_payload(_text, _charset)
diff -r b0087e17cd5e Lib/test/test_email/test_email.py
--- a/Lib/test/test_email/test_email.py	Fri Jul 01 17:57:30 2016 +0300
+++ b/Lib/test/test_email/test_email.py	Sat Jul 02 23:24:17 2016 +0200
@@ -1652,9 +1652,12 @@
         eq(msg.get_charset().input_charset, 'us-ascii')
         eq(msg['content-type'], 'text/plain; charset="us-ascii"')
         # Also accept a Charset instance
-        msg = MIMEText('hello there', _charset=Charset('utf-8'))
+        charset = Charset('utf-8')
+        charset.body_encoding = None
+        msg = MIMEText('hello there', _charset=charset)
         eq(msg.get_charset().input_charset, 'utf-8')
         eq(msg['content-type'], 'text/plain; charset="utf-8"')
+        eq(msg.get_payload(), 'hello there')
 
     def test_7bit_input(self):
         eq = self.assertEqual