diff --git a/include/event2/bufferevent.h b/include/event2/bufferevent.h
index 0067f248..ffe14738 100644
--- a/include/event2/bufferevent.h
+++ b/include/event2/bufferevent.h
@@ -245,6 +245,8 @@ int bufferevent_read_buffer(struct bufferevent *bufev, struct evbuffer *buf);
 /**
    Returns the input buffer.
 
+   The user MUST NOT set the callback on this buffer.
+
    @param bufev the buffervent from which to get the evbuffer
    @return the evbuffer object for the input buffer
  */
@@ -254,6 +256,8 @@ struct evbuffer *bufferevent_get_input(struct bufferevent *bufev);
 /**
    Returns the outut buffer.
 
+   The user MUST NOT set the callback on this buffer.
+
    When filters are being used, the filters need to be manually
    triggered if the output buffer was manipulated.