diff --git a/scripts/mbedtls_dev/test_case.py b/scripts/mbedtls_dev/test_case.py
index c476d1e..d01e143 100644
--- a/scripts/mbedtls_dev/test_case.py
+++ b/scripts/mbedtls_dev/test_case.py
@@ -19,15 +19,9 @@
 import binascii
 import os
 import sys
-from typing import Any, Iterable, List, Optional
-import typing_extensions #pylint: disable=import-error
+from typing import Iterable, List, Optional
 
-class Writable(typing_extensions.Protocol):
-    """Abstract class for typing hints."""
-    # pylint: disable=no-self-use,too-few-public-methods,unused-argument
-    def write(self, text: str) -> Any:
-        ...
-
+from mbedtls_dev import typing_util
 
 def hex_string(data: bytes) -> str:
     return '"' + binascii.hexlify(data).decode('ascii') + '"'
@@ -70,7 +64,7 @@
         if self.function is None:
             raise MissingFunction
 
-    def write(self, out: Writable) -> None:
+    def write(self, out: typing_util.Writable) -> None:
         """Write the .data file paragraph for this test case.
 
         The output starts and ends with a single newline character. If the
diff --git a/scripts/mbedtls_dev/typing_util.py b/scripts/mbedtls_dev/typing_util.py
new file mode 100644
index 0000000..4c34449
--- /dev/null
+++ b/scripts/mbedtls_dev/typing_util.py
@@ -0,0 +1,39 @@
+"""Auxiliary definitions used in type annotations.
+"""
+
+# Copyright The Mbed TLS Contributors
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from typing import Any
+
+# The typing_extensions module is necessary for type annotations that are
+# checked with mypy. It is only used for type annotations or to define
+# things that are themselves only used for type annotations. It is not
+# available on a default Python installation. Therefore, try loading
+# what we need from it for the sake of mypy (which depends on, or comes
+# with, typing_extensions), and if not define substitutes that lack the
+# static type information but are good enough at runtime.
+try:
+    from typing_extensions import Protocol #pylint: disable=import-error
+except ImportError:
+    class Protocol: #type: ignore
+        #pylint: disable=too-few-public-methods
+        pass
+
+class Writable(Protocol):
+    """Abstract class for typing hints."""
+    # pylint: disable=no-self-use,too-few-public-methods,unused-argument
+    def write(self, text: str) -> Any:
+        ...