diff --git a/Include/node.h b/Include/node.h
index 8704da8..517c3dc 100644
--- a/Include/node.h
+++ b/Include/node.h
@@ -20,7 +20,7 @@
 PyAPI_FUNC(int) PyNode_AddChild(node *n, int type,
                                       char *str, int lineno, int col_offset);
 PyAPI_FUNC(void) PyNode_Free(node *n);
-Py_ssize_t _PyNode_SizeOf(node *n);
+PyAPI_FUNC(Py_ssize_t) _PyNode_SizeOf(node *n);
 
 /* Node access functions */
 #define NCH(n)		((n)->n_nchildren)