diff --git a/Include/cpython/initconfig.h b/Include/cpython/initconfig.h
index 8326c23..df93a55 100644
--- a/Include/cpython/initconfig.h
+++ b/Include/cpython/initconfig.h
@@ -409,6 +409,10 @@
 
     /* If equal to 0, stop Python initialization before the "main" phase */
     int _init_main;
+
+    /* If non-zero, disallow threads, subprocesses, and fork.
+       Default: 0. */
+    int _isolated_interpreter;
 } PyConfig;
 
 PyAPI_FUNC(void) PyConfig_InitPythonConfig(PyConfig *config);
diff --git a/Include/cpython/pylifecycle.h b/Include/cpython/pylifecycle.h
index a01e9c9..eb523b8 100644
--- a/Include/cpython/pylifecycle.h
+++ b/Include/cpython/pylifecycle.h
@@ -65,6 +65,8 @@
 PyAPI_FUNC(int) _Py_LegacyLocaleDetected(int warn);
 PyAPI_FUNC(char *) _Py_SetLocaleFromEnv(int category);
 
+PyAPI_FUNC(PyThreadState *) _Py_NewInterpreter(int isolated_subinterpreter);
+
 #ifdef __cplusplus
 }
 #endif