diff --git a/Lib/email/test/test_email.py b/Lib/email/test/test_email.py
index 65b3ebd..8f4ef20 100644
--- a/Lib/email/test/test_email.py
+++ b/Lib/email/test/test_email.py
@@ -20,7 +20,7 @@ import email
 from email.charset import Charset
 from email.header import Header, decode_header, make_header
 from email.parser import Parser, HeaderParser
-from email.generator import Generator, DecodedGenerator
+from email.generator import Generator, DecodedGenerator, BytesGenerator
 from email.message import Message
 from email.mime.application import MIMEApplication
 from email.mime.audio import MIMEAudio
@@ -1276,6 +1276,51 @@ Blah blah blah
 """)
 
 
+class TestFromManglingBytes(unittest.TestCase):
+    # See issue #15249
+
+    def setUp(self):
+        # Don't use MIMEText, because it tries to encode the payload
+        # automatically. We want the surrogates to emulate what
+        # BytesParser would have produced.
+        self.msg = Message()
+        self.msg['Content-Type'] = 'text/plain; charset="utf-8"'
+        self.msg['MIME-Version'] = '1.0'
+        self.msg['Content-Transfer-Encoding'] = '8bit'
+        self.msg['From'] = 'aaa@bbb.org'
+
+        # Escape non-ASCII with surrogates. This is what BytesParser
+        # does.
+        text = b'From R\xc3\xb6lli\n'.decode('ascii', 'surrogateescape')
+        self.msg.set_payload(text)
+
+    def test_mangled_from(self):
+        b = BytesIO()
+        g = BytesGenerator(b, mangle_from_=True)
+        g.flatten(self.msg)
+        self.assertEqual(b.getvalue(), b'''\
+Content-Type: text/plain; charset="utf-8"
+MIME-Version: 1.0
+Content-Transfer-Encoding: 8bit
+From: aaa@bbb.org
+
+>From R\xc3\xb6lli
+''')
+
+    def test_dont_mangle_from(self):
+        b = BytesIO()
+        g = BytesGenerator(b, mangle_from_=False)
+        g.flatten(self.msg)
+        self.assertEqual(b.getvalue(), b'''\
+Content-Type: text/plain; charset="utf-8"
+MIME-Version: 1.0
+Content-Transfer-Encoding: 8bit
+From: aaa@bbb.org
+
+From R\xc3\xb6lli
+''')
+
+
 
 # Test the basic MIMEAudio class
 class TestMIMEAudio(unittest.TestCase):