diff --git a/Lib/cgi.py b/Lib/cgi.py
index 233a496..b44a6c3 100755
--- a/Lib/cgi.py
+++ b/Lib/cgi.py
@@ -721,10 +721,6 @@ class FieldStorage:
             parser.feed(hdr_text.decode(self.encoding, self.errors))
             headers = parser.close()
 
-            # Some clients add Content-Length for part headers, ignore them
-            if 'content-length' in headers:
-                del headers['content-length']
-
             part = klass(self.fp, headers, ib, environ, keep_blank_values,
                          strict_parsing,self.limit-self.bytes_read,
                          self.encoding, self.errors)
@@ -893,7 +889,7 @@ class FieldStorage:
         which unlinks the temporary files you have created.
 
         """
-        if self._binary_file:
+        if self._binary_file or self.length >= 0:
             return tempfile.TemporaryFile("wb+")
         else:
             return tempfile.TemporaryFile("w+",
diff --git a/Lib/test/test_cgi.py b/Lib/test/test_cgi.py
index 6373221..ce702da 100644
--- a/Lib/test/test_cgi.py
+++ b/Lib/test/test_cgi.py
@@ -343,7 +343,20 @@ Larry
         fs = cgi.FieldStorage(fp, environ=env, encoding="latin-1")
         self.assertEqual(len(fs.list), 1)
         self.assertEqual(fs.list[0].name, 'submit-name')
-        self.assertEqual(fs.list[0].value, 'Larry')
+        self.assertEqual(fs.list[0].value, b'Larry')
+
+    def test_fieldstorage_not_multipart(self):
+        POSTDATA = b'{"name": "Bert"}'
+
+        env = {
+            'REQUEST_METHOD': 'POST',
+            'CONTENT_TYPE': 'text/plain',
+            'CONTENT_LENGTH': str(len(POSTDATA))
+        }
+        fp = BytesIO(POSTDATA)
+        fs = cgi.FieldStorage(fp, environ=env)
+        self.assertEqual(fs.list, None)
+        self.assertEqual(fs.value, b'{"name": "Bert"}')
 
     def test_fieldstorage_as_context_manager(self):
         fp = BytesIO(b'x' * 10)