diff --git a/Lib/test/script_helper.py b/Lib/test/script_helper.py
--- a/Lib/test/script_helper.py
+++ b/Lib/test/script_helper.py
@@ -27,16 +27,20 @@ def _assert_python(expected_success, *ar
         # site-packages, and don't add the current directory to sys.path
         cmd_line.append('-I')
     elif not env_vars:
         # ignore Python environment variables
         cmd_line.append('-E')
     # Need to preserve the original environment, for in-place testing of
     # shared library builds.
     env = os.environ.copy()
+    # set TERM='' unless the TERM environment variable is passed explicitly
+    # see issues 11390 and 18300
+    if 'TERM' not in env_vars:
+        env['TERM'] = ''
     # But a special flag that can be set to override -- in this case, the
     # caller is responsible to pass the full environment.
     if env_vars.pop('__cleanenv', None):
         env = {}
     env.update(env_vars)
     cmd_line.extend(args)
     p = subprocess.Popen(cmd_line, stdin=subprocess.PIPE,
                          stdout=subprocess.PIPE, stderr=subprocess.PIPE,