diff --git a/src/module.c b/src/module.c
index 275ee4344..ab614c529 100644
--- a/src/module.c
+++ b/src/module.c
@@ -5389,6 +5389,7 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(ReplySetArrayLength);
     REGISTER_API(ReplyWithString);
     REGISTER_API(ReplyWithStringBuffer);
+    REGISTER_API(ReplyWithCString);
     REGISTER_API(ReplyWithNull);
     REGISTER_API(ReplyWithCallReply);
     REGISTER_API(ReplyWithDouble);
diff --git a/src/networking.c b/src/networking.c
index 9ff2afd8d..7bdd3c474 100644
--- a/src/networking.c
+++ b/src/networking.c
@@ -2468,7 +2468,6 @@ void flushSlavesOutputBuffers(void) {
     listRewind(server.slaves,&li);
     while((ln = listNext(&li))) {
         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
@@ -2477,9 +2476,8 @@ void flushSlavesOutputBuffers(void) {
          * This is what we want since slaves in this state should not receive
          * writes before the first ACK (to know the reason, grep for this
          * flag in this file). */
-        events = aeGetFileEvents(server.el,slave->fd);
-        if (events & AE_WRITABLE &&
-            slave->replstate == SLAVE_STATE_ONLINE &&
+        if (slave->replstate == SLAVE_STATE_ONLINE &&
+            !slave->repl_put_online_on_ack &&
             clientHasPendingReplies(slave))
         {
             writeToClient(slave->fd,slave,0);