diff --git a/src/typing_extensions.py b/src/typing_extensions.py
index cce31f8..b032530 100644
--- a/src/typing_extensions.py
+++ b/src/typing_extensions.py
@@ -440,7 +440,39 @@ else:
 Counter = typing.Counter
 ChainMap = typing.ChainMap
 AsyncGenerator = typing.AsyncGenerator
-NewType = typing.NewType
+if sys.version_info >= (3, 10):
+    NewType = typing.NewType
+else:
+    def NewType(name, tp):
+        """Create a new type with a distinct runtime representation.
+        The returned type is a simple subclass of the given type,
+        which allows for separate type checking while being
+        indistinguishable at runtime from the original type.
+        """
+        def __new__(cls, value):
+            return tp(value)
+        
+        def __init_subclass__(subclass, **kwargs):
+            # Prevent subclassing of NewType instances
+            raise TypeError(
+                "Cannot subclass an instance of NewType. Perhaps you were looking for: "
+                "`ProUserId = NewType('ProUserId', UserId)"
+            )
+        
+        # To keep the class lightweight we avoid creating a metaclass.
+        # The class is just a simple subclass of `tp`.
+        cls = type.__new__(type, name, (tp,), {
+            '__module__': None,
+            '__doc__': '',
+            '__annotations__': {},
+            '__new__': staticmethod(__new__),
+            '__init_subclass__': __init_subclass__,
+        })
+        # Make the class pickleable by providing a __reduce__ method.
+        def __reduce__(self):
+            return (NewType, (name, tp))
+        cls.__reduce__ = __reduce__
+        return cls
 Text = typing.Text
 TYPE_CHECKING = typing.TYPE_CHECKING