diff --git a/Lib/ntpath.py b/Lib/ntpath.py
index 923a458a407097..5309f41e386c60 100644
--- a/Lib/ntpath.py
+++ b/Lib/ntpath.py
@@ -243,13 +243,13 @@ def split(p):
 def splitext(p):
     p = os.fspath(p)
     if isinstance(p, bytes):
-        seps = (b'\\', b'/')
+        prefixes = (b'\\\\', b'//', b'\\/', b'/\\')
         root, ext = genericpath._splitext(p, b'\\', b'/', b'.')
     else:
-        seps = ('\\', '/')
+        prefixes = ('\\\\', '//', '\\/', '/\\')
         root, ext = genericpath._splitext(p, '\\', '/', '.')
-    if (ext and root[:1] in seps and root[1:2] in seps and
-        root.count(seps[0], 2) + root.count(seps[1], 2) <= 1):
+    if ext and root.startswith(prefixes) and not splitroot(root)[2]:
+        # \\server.ext or \\server\share.ext, but not \\server\share\path.ext
         return p, p[:0]
     return root, ext
 splitext.__doc__ = genericpath._splitext.__doc__
diff --git a/Lib/test/test_ntpath.py b/Lib/test/test_ntpath.py
index 696a6a621ffa46..94d482abeee43a 100644
--- a/Lib/test/test_ntpath.py
+++ b/Lib/test/test_ntpath.py
@@ -109,6 +109,15 @@ def test_splitext(self):
         tester(r'ntpath.splitext("//server.ext")',
                (r'//server.ext', ''))
 
+        tester(r'ntpath.splitext("\\?\UNC\server\share.ext")',
+               (r'\\?\UNC\server\share.ext', ''))
+        tester(r'ntpath.splitext("//?/UNC/server/share.ext")',
+               (r'//?/UNC/server/share.ext', ''))
+        tester(r'ntpath.splitext("\\?\UNC\server.ext")',
+               (r'\\?\UNC\server.ext', ''))
+        tester(r'ntpath.splitext("//?/UNC/server.ext")',
+               (r'//?/UNC/server.ext', ''))
+
         tester(r'ntpath.splitext("\\server\share\file.ext")',
                (r'\\server\share\file', '.ext'))
         tester(r'ntpath.splitext("//server/share/file.ext")',
@@ -117,6 +126,10 @@ def test_splitext(self):
                (r'\\server\share/file', '.ext'))
         tester(r'ntpath.splitext("//server/share\file.ext")',
                (r'//server/share\file', '.ext'))
+        tester(r'ntpath.splitext("\\?\UNC\server\share\file.ext")',
+               (r'\\?\UNC\server\share\file', '.ext'))
+        tester(r'ntpath.splitext("//?/UNC/server/share/file.ext")',
+               (r'//?/UNC/server/share/file', '.ext'))
 
     def test_splitdrive(self):
         tester("ntpath.splitdrive('')", ('', ''))