diff --git a/src/networking.c b/src/networking.c
index 782dc6c4..336561e1 100644
--- a/src/networking.c
+++ b/src/networking.c
@@ -1668,6 +1668,12 @@ void flushSlavesOutputBuffers(void) {
         client *slave = listNodeValue(ln);
         int events;
 
+        /* Note that the following will not flush output buffers of slaves
+         * in STATE_ONLINE but having put_online_on_ack set to true: in this
+         * case the writable event is never installed, since the purpose
+         * of put_online_on_ack is to postpone the moment it is installed.
+         * This is what we want since slaves in this state should not receive
+         * writes before the first ACK. */
         events = aeGetFileEvents(server.el,slave->fd);
         if (events & AE_WRITABLE &&
             slave->replstate == SLAVE_STATE_ONLINE &&