diff --git a/scripts/mbedtls_dev/test_case.py b/scripts/mbedtls_dev/test_case.py
index 6a46e42..d0afa59 100644
--- a/scripts/mbedtls_dev/test_case.py
+++ b/scripts/mbedtls_dev/test_case.py
@@ -92,9 +92,11 @@
     """
     if caller is None:
         caller = os.path.basename(sys.argv[0])
-    with open(filename, 'w') as out:
+    tempfile = filename + '.new'
+    with open(tempfile, 'w') as out:
         out.write('# Automatically generated by {}. Do not edit!\n'
                   .format(caller))
         for tc in test_cases:
             tc.write(out)
         out.write('\n# End of automatically generated file.\n')
+    os.replace(tempfile, filename)