diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index e8c14c2f8fe..0a82cb7e35a 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -164,6 +164,19 @@ class ProxyTests(unittest.TestCase):
         self.assertTrue(urllib.proxy_bypass_environment('anotherdomain.com:8888'))
         self.assertTrue(urllib.proxy_bypass_environment('newdomain.com:1234'))
 
+    def test_proxy_bypass_environment_host_match(self):
+        bypass = urllib.proxy_bypass_environment
+        self.env.set('NO_PROXY',
+            'localhost, anotherdomain.com, newdomain.com:1234')
+        self.assertTrue(bypass('localhost'))
+        self.assertTrue(bypass('LocalHost'))                 # MixedCase
+        self.assertTrue(bypass('LOCALHOST'))                 # UPPERCASE
+        self.assertTrue(bypass('newdomain.com:1234'))
+        self.assertTrue(bypass('anotherdomain.com:8888'))
+        self.assertTrue(bypass('www.newdomain.com:1234'))
+        self.assertFalse(bypass('prelocalhost'))
+        self.assertFalse(bypass('newdomain.com'))            # no port
+        self.assertFalse(bypass('newdomain.com:1235'))       # wrong port
 
 class ProxyTests_withOrderedEnv(unittest.TestCase):
 
diff --git a/Lib/urllib.py b/Lib/urllib.py
index 6d17e6ff23a..055707ff1ef 100644
--- a/Lib/urllib.py
+++ b/Lib/urllib.py
@@ -1423,8 +1423,12 @@ def proxy_bypass_environment(host, proxies=None):
     # check if the host ends with any of the DNS suffixes
     no_proxy_list = [proxy.strip() for proxy in no_proxy.split(',')]
     for name in no_proxy_list:
-        if name and (hostonly.endswith(name) or host.endswith(name)):
-            return 1
+        if name:
+            name = re.escape(name)
+            pattern = r'(.+\.)?%s$' % name
+            if (re.match(pattern, hostonly, re.I)
+                    or re.match(pattern, host, re.I)):
+                return 1
     # otherwise, don't bypass
     return 0
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 6f29bca862d..ea36439efd3 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -77,6 +77,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #26864: In urllib, change the proxy bypass host checking against
+  no_proxy to be case-insensitive, and to not match unrelated host names that
+  happen to have a bypassed hostname as a suffix.  Patch by Xiang Zhang.
+
 - Issue #26804: urllib will prefer lower_case proxy environment variables over
   UPPER_CASE or Mixed_Case ones. Patch contributed by Hans-Peter Jansen.