diff --git a/Lib/email/test/test_email.py b/Lib/email/test/test_email.py
--- a/Lib/email/test/test_email.py
+++ b/Lib/email/test/test_email.py
@@ -4685,6 +4685,26 @@
         self.assertFalse(isinstance(param, tuple))
         self.assertEqual(param, "us-ascii'en-us'Frank's Document")
 
+    def test_rfc2231_missing_tick(self):
+        m = '''\
+Content-Disposition: inline;
+\tfilename*0*="'This%20is%20broken";
+'''
+        msg = email.message_from_string(m)
+        self.assertEqual(
+            msg.get_filename(),
+            "'This is broken")
+
+    def test_rfc2231_missing_tick_with_encoded_non_ascii(self):
+        m = '''\
+Content-Disposition: inline;
+\tfilename*0*="'This%20is%E2broken";
+'''
+        msg = email.message_from_string(m)
+        self.assertEqual(
+            msg.get_filename(),
+            "'This is\ufffdbroken")
+
     def test_rfc2231_no_extended_values(self):
         eq = self.assertEqual
         m = """\
diff --git a/Lib/email/utils.py b/Lib/email/utils.py
--- a/Lib/email/utils.py
+++ b/Lib/email/utils.py
@@ -298,6 +298,10 @@
     # object.  We do not want bytes() normal utf-8 decoder, we want a straight
     # interpretation of the string as character bytes.
     charset, language, text = value
+    if charset is None:
+        # Issue 17369: if charset/lang is None, decode_rfc2231 couldn't parse
+        # the value, so use the fallback_charset.
+        charset = fallback_charset
     rawbytes = bytes(text, 'raw-unicode-escape')
     try:
         return str(rawbytes, charset, errors)