diff --git a/django/core/mail.py b/django/core/mail.py
index e9d8a150a1..2f252df724 100644
--- a/django/core/mail.py
+++ b/django/core/mail.py
@@ -62,22 +62,23 @@ def make_msgid(idstring=None):
 class BadHeaderError(ValueError):
     pass
 
-class SafeHeaderMixin(object):
+class SafeMIMEText(MIMEText):
     def __setitem__(self, name, val):
         "Forbids multi-line headers, to prevent header injection."
         if '\n' in val or '\r' in val:
             raise BadHeaderError, "Header values can't contain newlines (got %r for header %r)" % (val, name)
         if name == "Subject":
             val = Header(val, settings.DEFAULT_CHARSET)
-        # Note: using super() here is safe; any __setitem__ overrides must use
-        # the same argument signature.
-        super(SafeHeaderMixin, self).__setitem__(name, val)
+        MIMEText.__setitem__(self, name, val)
 
-class SafeMIMEText(MIMEText, SafeHeaderMixin):
-    pass
-
-class SafeMIMEMultipart(MIMEMultipart, SafeHeaderMixin):
-    pass
+class SafeMIMEMultipart(MIMEMultipart):
+    def __setitem__(self, name, val):
+        "Forbids multi-line headers, to prevent header injection."
+        if '\n' in val or '\r' in val:
+            raise BadHeaderError, "Header values can't contain newlines (got %r for header %r)" % (val, name)
+        if name == "Subject":
+            val = Header(val, settings.DEFAULT_CHARSET)
+        MIMEMultipart.__setitem__(self, name, val)
 
 class SMTPConnection(object):
     """