diff --git a/graalpython/com.oracle.graal.python.cext/include/Python.h b/graalpython/com.oracle.graal.python.cext/include/Python.h
index a653aa8ea2..00e286ff9e 100644
--- a/graalpython/com.oracle.graal.python.cext/include/Python.h
+++ b/graalpython/com.oracle.graal.python.cext/include/Python.h
@@ -1,4 +1,4 @@
-/* Copyright (c) 2022, 2024, Oracle and/or its affiliates.
+/* Copyright (c) 2022, 2026, Oracle and/or its affiliates.
  * Copyright (C) 1996-2022 Python Software Foundation
  *
  * Licensed under the PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2
@@ -100,6 +100,7 @@ struct timeval;
 #include "pythonrun.h"
 #include "pylifecycle.h"
 #include "ceval.h"
+#include "intrcheck.h"
 #include "sysmodule.h"
 #include "osmodule.h"
 #include "import.h"
diff --git a/graalpython/com.oracle.graal.python.cext/include/intrcheck.h b/graalpython/com.oracle.graal.python.cext/include/intrcheck.h
new file mode 100644
index 0000000000..2c940799b2
--- /dev/null
+++ b/graalpython/com.oracle.graal.python.cext/include/intrcheck.h
@@ -0,0 +1,34 @@
+/* Copyright (c) 2026, Oracle and/or its affiliates.
+ * Copyright (C) 1996-2020 Python Software Foundation
+ *
+ * Licensed under the PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2
+ */
+
+#ifndef Py_INTRCHECK_H
+#define Py_INTRCHECK_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+PyAPI_FUNC(int) PyOS_InterruptOccurred(void);
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03070000
+PyAPI_FUNC(void) PyOS_BeforeFork(void);
+PyAPI_FUNC(void) PyOS_AfterFork_Parent(void);
+PyAPI_FUNC(void) PyOS_AfterFork_Child(void);
+#endif
+/* Deprecated, please use PyOS_AfterFork_Child() instead */
+Py_DEPRECATED(3.7) PyAPI_FUNC(void) PyOS_AfterFork(void);
+
+#ifndef Py_LIMITED_API
+PyAPI_FUNC(int) _PyOS_IsMainThread(void);
+
+#ifdef MS_WINDOWS
+/* windows.h is not included by Python.h so use void* instead of HANDLE */
+PyAPI_FUNC(void*) _PyOS_SigintEvent(void);
+#endif
+#endif /* !Py_LIMITED_API */
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTRCHECK_H */
diff --git a/graalpython/com.oracle.graal.python.cext/src/pylifecycle.c b/graalpython/com.oracle.graal.python.cext/src/pylifecycle.c
index 77e295c1fc..16f474b73d 100644
--- a/graalpython/com.oracle.graal.python.cext/src/pylifecycle.c
+++ b/graalpython/com.oracle.graal.python.cext/src/pylifecycle.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * The Universal Permissive License (UPL), Version 1.0
@@ -73,6 +73,36 @@ _Py_IsFinalizing(void)
     return graalpy_finalizing;
 }
 
+static void
+graalpy_fork_not_supported(void)
+{
+    PyErr_SetString(PyExc_SystemError, "fork is not supported by GraalPy");
+}
+
+void
+PyOS_BeforeFork(void)
+{
+    graalpy_fork_not_supported();
+}
+
+void
+PyOS_AfterFork_Parent(void)
+{
+    graalpy_fork_not_supported();
+}
+
+void
+PyOS_AfterFork_Child(void)
+{
+    graalpy_fork_not_supported();
+}
+
+void
+PyOS_AfterFork(void)
+{
+    PyOS_AfterFork_Child();
+}
+
 void _Py_NO_RETURN  _Py_FatalErrorFunc(const char *func, const char *msg) {
     const char *prefix1 = "", *prefix2 = "";
     if (func) {
diff --git a/graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/cext/capi/CApiFunction.java b/graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/cext/capi/CApiFunction.java
index b1442d8123..12a452f965 100644
--- a/graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/cext/capi/CApiFunction.java
+++ b/graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/cext/capi/CApiFunction.java
@@ -855,10 +855,10 @@ public final class CApiFunction {
     @CApiBuiltin(name = "PyODict_DelItem", ret = Int, args = {PyObject, PyObject}, call = NotImplemented)
     @CApiBuiltin(name = "PyODict_New", ret = PyObject, args = {}, call = NotImplemented)
     @CApiBuiltin(name = "PyODict_SetItem", ret = Int, args = {PyObject, PyObject, PyObject}, call = NotImplemented)
-    @CApiBuiltin(name = "PyOS_AfterFork", ret = Void, args = {}, call = NotImplemented)
-    @CApiBuiltin(name = "PyOS_AfterFork_Child", ret = Void, args = {}, call = NotImplemented)
-    @CApiBuiltin(name = "PyOS_AfterFork_Parent", ret = Void, args = {}, call = NotImplemented)
-    @CApiBuiltin(name = "PyOS_BeforeFork", ret = Void, args = {}, call = NotImplemented)
+    @CApiBuiltin(name = "PyOS_AfterFork", ret = Void, args = {}, call = CImpl)
+    @CApiBuiltin(name = "PyOS_AfterFork_Child", ret = Void, args = {}, call = CImpl)
+    @CApiBuiltin(name = "PyOS_AfterFork_Parent", ret = Void, args = {}, call = CImpl)
+    @CApiBuiltin(name = "PyOS_BeforeFork", ret = Void, args = {}, call = CImpl)
     @CApiBuiltin(name = "PyOS_InterruptOccurred", ret = Int, args = {}, call = NotImplemented)
     @CApiBuiltin(name = "PyOS_Readline", ret = CHAR_PTR, args = {FILE_PTR, FILE_PTR, ConstCharPtrAsTruffleString}, call = NotImplemented)
     @CApiBuiltin(name = "PyOS_getsig", ret = PY_OS_SIGHANDLER, args = {Int}, call = NotImplemented)
diff --git a/mx.graalpython/copyrights/overrides b/mx.graalpython/copyrights/overrides
index 24cdf56daf..89a9959ddd 100644
--- a/mx.graalpython/copyrights/overrides
+++ b/mx.graalpython/copyrights/overrides
@@ -182,6 +182,7 @@ graalpython/com.oracle.graal.python.cext/include/internal/pycore_typeobject.h,py
 graalpython/com.oracle.graal.python.cext/include/internal/pycore_ucnhash.h,python.copyright
 graalpython/com.oracle.graal.python.cext/include/internal/pycore_unicodeobject.h,python.copyright
 graalpython/com.oracle.graal.python.cext/include/internal/pycore_warnings.h,python.copyright
+graalpython/com.oracle.graal.python.cext/include/intrcheck.h,python.copyright
 graalpython/com.oracle.graal.python.cext/include/iterobject.h,python.copyright
 graalpython/com.oracle.graal.python.cext/include/listobject.h,python.copyright
 graalpython/com.oracle.graal.python.cext/include/longobject.h,python.copyright