diff --git a/Lib/email/generator.py b/Lib/email/generator.py
index 717a6c6378b..eb710447006 100644
--- a/Lib/email/generator.py
+++ b/Lib/email/generator.py
@@ -208,7 +208,8 @@ class Generator:
             # Create a boundary that doesn't appear in any of the
             # message texts.
             alltext = NL.join(msgtexts)
-            msg.set_boundary(self._make_boundary(alltext))
+            boundary = _make_boundary(alltext)
+            msg.set_boundary(boundary)
         # If there's a preamble, write it out, with a trailing CRLF
         if msg.preamble is not None:
             print >> self._fp, msg.preamble
diff --git a/Lib/email/test/test_email.py b/Lib/email/test/test_email.py
index 7a1d699cf62..358b6a7ef01 100644
--- a/Lib/email/test/test_email.py
+++ b/Lib/email/test/test_email.py
@@ -179,6 +179,17 @@ class TestMessageAPI(TestEmailBase):
         self.assertRaises(Errors.HeaderParseError,
                           msg.set_boundary, 'BOUNDARY')
 
+    def test_make_boundary(self):
+        msg = MIMEMultipart('form-data')
+        # Note that when the boundary gets created is an implementation
+        # detail and might change.
+        self.assertEqual(msg.items()[0][1], 'multipart/form-data')
+        # Trigger creation of boundary
+        msg.as_string()
+        self.assertEqual(msg.items()[0][1][:33],
+                        'multipart/form-data; boundary="==')
+        # XXX: there ought to be tests of the uniqueness of the boundary, too.
+
     def test_message_rfc822_only(self):
         # Issue 7970: message/rfc822 not in multipart parsed by
         # HeaderParser caused an exception when flattened.