diff --git a/Include/warnings.h b/Include/warnings.h
index f54eabd..c84cb9f 100644
--- a/Include/warnings.h
+++ b/Include/warnings.h
@@ -7,6 +7,7 @@
 PyAPI_FUNC(PyObject*) _PyWarnings_Init(void);
 
 PyAPI_FUNC(int) PyErr_WarnEx(PyObject *, const char *, Py_ssize_t);
+PyAPI_FUNC(int) PyErr_WarnFormat(PyObject *, Py_ssize_t, const char *, ...);
 PyAPI_FUNC(int) PyErr_WarnExplicit(PyObject *, const char *, const char *, int,
                                     const char *, PyObject *);