diff --git a/Lib/test/test_ctypes/test_funcptr.py b/Lib/test/test_ctypes/test_funcptr.py
index b4c27809b5333d..b90f019dc67bed 100644
--- a/Lib/test/test_ctypes/test_funcptr.py
+++ b/Lib/test/test_ctypes/test_funcptr.py
@@ -199,6 +199,14 @@ def test_wrap_dll_function_str_ann(self):
         version = wrap_str_ann.Py_GetVersion()
         self.assertIsInstance(version, bytes)
 
+    def test_invalid_argtypes(self):
+        libc = CDLL(None)
+
+        PRINTF_PROTO = CFUNCTYPE(c_int, ctypes.c_char_p)
+        c_printf = PRINTF_PROTO(("printf", libc), ((1,),))
+        c_printf.argtypes = (c_char_p, c_int)
+        with self.assertRaises(TypeError):
+            c_printf(b"Hello\n")
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/Misc/NEWS.d/next/Library/2025-08-27-01-04-38.gh-issue-138008.iCEhZ9.rst b/Misc/NEWS.d/next/Library/2025-08-27-01-04-38.gh-issue-138008.iCEhZ9.rst
new file mode 100644
index 00000000000000..53e394547de84a
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-08-27-01-04-38.gh-issue-138008.iCEhZ9.rst
@@ -0,0 +1 @@
+Fix segfaults in _cyptes during _build_callargs.
diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index ae49cbf3e57da7..f6bf40c07169a4 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -4382,7 +4382,11 @@ _build_callargs(ctypes_state *st, PyCFuncPtrObject *self, PyObject *argtypes,
     callargs = PyTuple_New(len); /* the argument tuple we build */
     if (callargs == NULL)
         return NULL;
-
+    if (!_validate_paramflags(st, Py_TYPE(self), paramflags, argtypes)) {
+        PyErr_SetString(PyExc_TypeError,
+                        "the current argument is invalid");
+        goto error;
+    }
 #ifdef MS_WIN32
     /* For a COM method, skip the first arg */
     if (self->index) {