diff --git a/scrapy/core/downloader/handlers/http11.py b/scrapy/core/downloader/handlers/http11.py
index 25cb3ec62..073f35891 100644
--- a/scrapy/core/downloader/handlers/http11.py
+++ b/scrapy/core/downloader/handlers/http11.py
@@ -98,8 +98,9 @@ class TunnelingTCP4ClientEndpoint(TCP4ClientEndpoint):
     with this endpoint comes from the pool and a CONNECT has already been issued
     for it.
     """
-
-    _responseMatcher = re.compile(br'HTTP/1\.. (?P<status>\d{3})(?P<reason>.{,32})')
+    _truncatedLength = 1000
+    _responseAnswer = r'HTTP/1\.. (?P<status>\d{3})(?P<reason>.{,' + str(_truncatedLength) + r'})'
+    _responseMatcher = re.compile(_responseAnswer.encode())
 
     def __init__(self, reactor, host, port, proxyConf, contextFactory, timeout=30, bindAddress=None):
         proxyHost, proxyPort, self._proxyAuthHeader = proxyConf
@@ -144,7 +145,7 @@ class TunnelingTCP4ClientEndpoint(TCP4ClientEndpoint):
                 extra = {'status': int(respm.group('status')),
                          'reason': respm.group('reason').strip()}
             else:
-                extra = rcvd_bytes[:32]
+                extra = rcvd_bytes[:self._truncatedLength]
             self._tunnelReadyDeferred.errback(
                 TunnelError('Could not open CONNECT tunnel with proxy '
                             f'{self._host}:{self._port} [{extra!r}]')