diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index 3bf9ea7..49e2a2c 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -231,6 +231,19 @@
         self.assertTrue(urllib.request.proxy_bypass_environment('anotherdomain.com:8888'))
         self.assertTrue(urllib.request.proxy_bypass_environment('newdomain.com:1234'))
 
+    def test_proxy_bypass_environment_host_match(self):
+        bypass = urllib.request.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/request.py b/Lib/urllib/request.py
index fc42d49..b28cd60 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -2432,8 +2432,12 @@
     # 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 e887e90..67c2a17 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -107,6 +107,11 @@
 Library
 -------
 
+- Issue #26864: In urllib.request, 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 #26634: recursive_repr() now sets __qualname__ of wrapper.  Patch by
   Xiang Zhang.