diff --git a/netlib/http/request.py b/netlib/http/request.py
index b9076c0f2..99662732e 100644
--- a/netlib/http/request.py
+++ b/netlib/http/request.py
@@ -1,5 +1,6 @@
 from __future__ import absolute_import, print_function, division
 
+import re
 import warnings
 
 import six
@@ -12,6 +13,10 @@ from .. import encoding
 from .headers import Headers
 from .message import Message, _native, _always_bytes, MessageData
 
+# This regex extracts & splits the host header into host and port.
+# Handles the edge case of IPv6 addresses containing colons.
+# https://bugzilla.mozilla.org/show_bug.cgi?id=45891
+host_header_re = re.compile(r"^(?P<host>[^:]+|\[.+\])(?::(?P<port>\d+))?$")
 
 class RequestData(MessageData):
     def __init__(self, first_line_format, method, scheme, host, port, path, http_version, headers=None, content=None,
@@ -159,6 +164,18 @@ class Request(Message):
     def url(self, url):
         self.scheme, self.host, self.port, self.path = utils.parse_url(url)
 
+    def _parse_host_header(self):
+        """Extract the host and port from Host header"""
+        if "host" not in self.headers:
+            return None, None
+        host, port = self.headers["host"], None
+        m = host_header_re.match(host)
+        if m:
+            host = m.group("host").strip("[]")
+            if m.group("port"):
+                port = int(m.group("port"))
+        return host, port
+
     @property
     def pretty_host(self):
         """
@@ -166,7 +183,13 @@ class Request(Message):
         This is useful in transparent mode where :py:attr:`host` is only an IP address,
         but may not reflect the actual destination as the Host header could be spoofed.
         """
-        return self.headers.get("host", self.host)
+        host, port = self._parse_host_header()
+        if not host:
+            return self.host
+        if not port:
+            port = 443 if self.scheme == 'https' else 80
+        # Prefer the original address if host header has an unexpected form
+        return host if port == self.port else self.host
 
     @property
     def pretty_url(self):
diff --git a/test/mitmproxy/test_flow.py b/test/mitmproxy/test_flow.py
index a593c8c3a..13ced2651 100644
--- a/test/mitmproxy/test_flow.py
+++ b/test/mitmproxy/test_flow.py
@@ -1035,7 +1035,7 @@ class TestRequest:
         assert r.url == "https://address:22/path"
 
         assert r.pretty_url == "https://address:22/path"
-        r.headers["Host"] = "foo.com"
+        r.headers["Host"] = "foo.com:22"
         assert r.url == "https://address:22/path"
         assert r.pretty_url == "https://foo.com:22/path"
 
diff --git a/test/netlib/http/test_request.py b/test/netlib/http/test_request.py
index b4ecfd4ee..5672259ed 100644
--- a/test/netlib/http/test_request.py
+++ b/test/netlib/http/test_request.py
@@ -104,25 +104,36 @@ class TestRequestUtils(object):
 
     def test_pretty_host(self):
         request = treq()
+        # Without host header
         assert request.pretty_host == "address"
         assert request.host == "address"
-        request.headers["host"] = "other"
+        # Same port as self.port (22)
+        request.headers["host"] = "other:22"
         assert request.pretty_host == "other"
+        # Different ports
+        request.headers["host"] = "other"
+        assert request.pretty_host == "address"
         assert request.host == "address"
+        # Empty host
         request.host = None
         assert request.pretty_host is None
         assert request.host is None
 
         # Invalid IDNA
-        request.headers["host"] = ".disqus.com"
+        request.headers["host"] = ".disqus.com:22"
         assert request.pretty_host == ".disqus.com"
 
     def test_pretty_url(self):
         request = treq()
+        # Without host header
         assert request.url == "http://address:22/path"
         assert request.pretty_url == "http://address:22/path"
-        request.headers["host"] = "other"
+        # Same port as self.port (22)
+        request.headers["host"] = "other:22"
         assert request.pretty_url == "http://other:22/path"
+        # Different ports
+        request.headers["host"] = "other"
+        assert request.pretty_url == "http://address:22/path"
 
     def test_pretty_url_authority(self):
         request = treq(first_line_format="authority")