@@ -144,7 +144,7 @@ pydoc-topics: build
 
 .PHONY: gettext
 gettext: BUILDER = gettext
-gettext: SPHINXOPTS += -d build/doctrees-gettext
+gettext: override SPHINXOPTS := -d build/doctrees-gettext $(SPHINXOPTS)
 gettext: build
 
 .PHONY: htmlview
 
@@ -963,7 +963,7 @@ def answer_challenge(connection, authkey: bytes):
                 f'Protocol error, expected challenge: {message=}')
     message = message[len(_CHALLENGE):]
     if len(message) < _MD5ONLY_MESSAGE_LENGTH:
-        raise AuthenticationError('challenge too short: {len(message)} bytes')
+        raise AuthenticationError(f'challenge too short: {len(message)} bytes')
     digest = _create_response(authkey, message)
     connection.send_bytes(digest)
     response = connection.recv_bytes(256)        # reject large message
 
@@ -1649,6 +1649,10 @@ def test_set___main___attrs(self):
             self.assertIs(after2, None)
             self.assertEqual(after3.type.__name__, 'AssertionError')
 
+            with self.assertRaises(ValueError):
+                # GH-127165: Embedded NULL characters broke the lookup
+                _interpreters.set___main___attrs(interpid, {"\x00": 1})
+
         with self.subTest('from C-API'):
             with self.interpreter_from_capi() as interpid:
                 with self.assertRaisesRegex(InterpreterError, 'unrecognized'):
 
@@ -342,6 +342,11 @@ _copy_string_obj_raw(PyObject *strobj, Py_ssize_t *p_size)
         return NULL;
     }
 
+    if (size != (Py_ssize_t)strlen(str)) {
+        PyErr_SetString(PyExc_ValueError, "found embedded NULL character");
+        return NULL;
+    }
+
     char *copied = PyMem_RawMalloc(size+1);
     if (copied == NULL) {
         PyErr_NoMemory();