diff --git a/Lib/http/client.py b/Lib/http/client.py
index 5aa178d7b127d90..9b57128b9b0a525 100644
--- a/Lib/http/client.py
+++ b/Lib/http/client.py
@@ -1023,6 +1023,7 @@ def _send_output(self, message_body=None, encode_chunked=False):
                 # is needed to allow the current position of mmap'ed
                 # files to be taken into account.
                 chunks = self._read_readable(message_body)
+                message_body.seek(0)
             else:
                 try:
                     # this is solely to check to see if message_body
diff --git a/Lib/test/test_urllib2_localnet.py b/Lib/test/test_urllib2_localnet.py
index 77dec0ce713ccb4..4f767ed9555c465 100644
--- a/Lib/test/test_urllib2_localnet.py
+++ b/Lib/test/test_urllib2_localnet.py
@@ -238,7 +238,29 @@ def do_GET(self):
             # Request Unauthorized
             self.do_AUTHHEAD()
 
-
+    def do_POST(self):
+        if not self.headers.get("Authorization", ""):
+            self.do_AUTHHEAD()
+            self.wfile.write(b"No Auth header received")
+        elif self.headers.get(
+                "Authorization", "") == "Basic " + self.ENCODED_AUTH:
+            encoding = self.headers.get("Transfer-Encoding")
+            if encoding is None:
+                length = int(self.headers.get("Content-Length"))
+            else:
+                assert encoding == "chunked"
+                length = int(self.rfile.readline(), 16)
+            request = self.rfile.read(length)
+            assert len(request) == length
+            if length > 0:
+                self.send_response(200, "OK")
+                self.end_headers()
+                self.wfile.write(request)
+            else:
+                self.send_response(400, "Empty request data")
+                self.end_headers()
+        else:
+            self.do_AUTHHEAD()
 
 # Proxy test infrastructure
 
@@ -314,6 +336,19 @@ def test_basic_auth_httperror(self):
         urllib.request.install_opener(urllib.request.build_opener(ah))
         self.assertRaises(urllib.error.HTTPError, urllib.request.urlopen, self.server_url)
 
+    def test_basic_auth_mmap_payload(self):
+        from mmap import mmap
+        data = "field=value".encode("ascii")
+        mem = mmap(-1, len(data))
+        mem[:] = data
+        auth_handler = urllib.request.HTTPBasicAuthHandler()
+        auth_handler.add_password(realm=self.REALM, uri=self.server_url,
+                                  user=self.USER, passwd=self.PASSWD)
+        opener = urllib.request.build_opener(auth_handler)
+        urllib.request.install_opener(opener)
+        response = opener.open(self.server_url, mem)
+        self.assertEqual(response.read(), data)
+
 
 class ProxyAuthTests(unittest.TestCase):
     URL = "http://localhost"
@@ -658,7 +693,6 @@ def test_line_iteration(self):
                              (index, len(lines[index]), len(line)))
         self.assertEqual(index + 1, len(lines))
 
-
 threads_key = None
 
 def setUpModule():
diff --git a/Misc/NEWS.d/next/Library/2019-02-13-18-51-31.bpo-5038.NWt7FW.rst b/Misc/NEWS.d/next/Library/2019-02-13-18-51-31.bpo-5038.NWt7FW.rst
new file mode 100644
index 000000000000000..b291779afc9b521
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-02-13-18-51-31.bpo-5038.NWt7FW.rst
@@ -0,0 +1,2 @@
+http lib allows mmap'ed files to be resent when the http server responds with 401 unauthorized or similar initial responses
+and the requests has to be resend.
\ No newline at end of file