diff --git a/Include/methodobject.h b/Include/methodobject.h
index 39272815b127f4..cfff05f803309e 100644
--- a/Include/methodobject.h
+++ b/Include/methodobject.h
@@ -24,7 +24,7 @@ typedef PyObject *(*PyCFunctionFastWithKeywords) (PyObject *,
                                                   PyObject *const *, Py_ssize_t,
                                                   PyObject *);
 typedef PyObject *(*PyCMethod)(PyObject *, PyTypeObject *, PyObject *const *,
-                               size_t, PyObject *);
+                               Py_ssize_t, PyObject *);
 
 // For backwards compatibility. `METH_FASTCALL` was added to the stable API in
 // 3.10 alongside `_PyCFunctionFastWithKeywords` and `_PyCFunctionFast`.
diff --git a/Misc/NEWS.d/next/C_API/2025-03-12-08-29-23.gh-issue-111178.Jny_YJ.rst b/Misc/NEWS.d/next/C_API/2025-03-12-08-29-23.gh-issue-111178.Jny_YJ.rst
new file mode 100644
index 00000000000000..a34ec01ccffc60
--- /dev/null
+++ b/Misc/NEWS.d/next/C_API/2025-03-12-08-29-23.gh-issue-111178.Jny_YJ.rst
@@ -0,0 +1,2 @@
+Fix :c:type:`PyCMethod` API: replace ``size_t nargs`` with ``Py_ssize_t nargs``
+in :c:type:`PyCMethod`. Patch by Victor Stinner.