diff --git a/src/if_python3.c b/src/if_python3.c
index ecca163..d540226 100644
--- a/src/if_python3.c
+++ b/src/if_python3.c
@@ -1256,6 +1256,10 @@
     if (PyLong_Check(idx))
     {
 	long n = PyLong_AsLong(idx);
+
+	if (CheckBuffer((BufferObject *) self))
+	    return -1;
+
 	return RBAsItem((BufferObject *)(self), n, val, 1,
 		    (Py_ssize_t)((BufferObject *)(self))->buf->b_ml.ml_line_count,
 		    NULL);