diff --git a/src/AsyncTCP.cpp b/src/AsyncTCP.cpp
index 7ed632a..9188098 100644
--- a/src/AsyncTCP.cpp
+++ b/src/AsyncTCP.cpp
@@ -598,30 +598,20 @@ bool AsyncClient::_sockIsWriteable(void)
         // Socket can accept some new data...
         xSemaphoreTake(_write_mutex, (TickType_t)portMAX_DELAY);
         if (_writeQueue.size() > 0) {
-            if (_writeQueue.front().written < _writeQueue.front().length) {
-                uint8_t * p = _writeQueue.front().data + _writeQueue.front().written;
-                size_t n = _writeQueue.front().length - _writeQueue.front().written;
-                errno = 0; ssize_t r = lwip_write(_socket, p, n);
-
-                if (r >= 0) {
-                    // Written some data into the socket
-                    _writeQueue.front().written += r;
-                    _writeSpaceRemaining += r;
-                    activity = true;
-                } else if (errno == EAGAIN || errno == EWOULDBLOCK) {
-                    // Socket is full, could not write anything
-                } else {
-                    hasErr = true;
-                    sent_errno = errno;
-                }
+            activity = _flushWriteQueue();
+            if (_writeQueue.front().write_errno != 0) {
+                hasErr = true;
+                sent_errno = _writeQueue.front().write_errno;
             }
 
             if (!hasErr && _writeQueue.front().written >= _writeQueue.front().length) {
                 // Buffer has been fully written to the socket
-                _rx_last_packet = millis();
+                if (_writeQueue.front().written_at > _rx_last_packet) {
+                    _rx_last_packet = _writeQueue.front().written_at;
+                }
                 if (_writeQueue.front().owned) ::free(_writeQueue.front().data);
                 sent_cb_length = _writeQueue.front().length;
-                sent_cb_delay = millis() - _writeQueue.front().queued_at;
+                sent_cb_delay = _writeQueue.front().written_at - _writeQueue.front().queued_at;
                 _writeQueue.pop_front();
             }
         }
@@ -639,6 +629,38 @@ bool AsyncClient::_sockIsWriteable(void)
     return activity;
 }
 
+bool AsyncClient::_flushWriteQueue(void)
+{
+    bool activity = false;
+
+    if (_socket == -1) return false;
+
+    auto & qwb = _writeQueue.front();
+
+    if (qwb.write_errno == 0 && qwb.written < qwb.length) {
+        uint8_t * p = qwb.data + qwb.written;
+        size_t n = qwb.length - qwb.written;
+        errno = 0; ssize_t r = lwip_write(_socket, p, n);
+
+        if (r >= 0) {
+            // Written some data into the socket
+            qwb.written += r;
+            _writeSpaceRemaining += r;
+            activity = true;
+
+            if (qwb.written >= qwb.length) {
+                qwb.written_at = millis();
+            }
+        } else if (errno == EAGAIN || errno == EWOULDBLOCK) {
+            // Socket is full, could not write anything
+        } else {
+            qwb.write_errno = errno;
+        }
+    }
+
+    return activity;
+}
+
 void AsyncClient::_sockIsReadable(void)
 {
     _rx_last_packet = millis();
@@ -766,6 +788,8 @@ size_t AsyncClient::add(const char* data, size_t size, uint8_t apiflags)
     n_entry.length = will_send;
     n_entry.written = 0;
     n_entry.queued_at = millis();
+    n_entry.written_at = 0;
+    n_entry.write_errno = 0;
 
     xSemaphoreTake(_write_mutex, (TickType_t)portMAX_DELAY);
     _writeQueue.push_back(n_entry);
@@ -778,7 +802,19 @@ size_t AsyncClient::add(const char* data, size_t size, uint8_t apiflags)
 
 bool AsyncClient::send()
 {
+    fd_set sockSet_w;
+    struct timeval tv;
+
+    FD_ZERO(&sockSet_w);
+    FD_SET(_socket, &sockSet_w);
+    tv.tv_sec = 0;
+    tv.tv_usec = 0;
+
     // TODO: data was already queued, what should be done here?
+    xSemaphoreTake(_write_mutex, (TickType_t)portMAX_DELAY);
+    int r = select(_socket + 1, NULL, &sockSet_w, NULL, &tv);
+    if (r > 0) _flushWriteQueue();
+    xSemaphoreGive(_write_mutex);
     return true;
 }
 
diff --git a/src/AsyncTCP.h b/src/AsyncTCP.h
index d922449..2e0f2ae 100644
--- a/src/AsyncTCP.h
+++ b/src/AsyncTCP.h
@@ -137,6 +137,12 @@ class AsyncClient : public AsyncSocketBase
     const char * errorToString(int8_t error);
 //    const char * stateToString();
 
+  protected:
+    bool _sockIsWriteable(void);
+    void _sockIsReadable(void);
+    void _sockPoll(void);
+    void _sockDelayedConnect(void);
+
   private:
 
     AcConnectHandler _connect_cb;
@@ -175,6 +181,8 @@ class AsyncClient : public AsyncSocketBase
       uint32_t  length;   // Length of data queued for write
       uint32_t  written;  // Length of data written to socket so far
       uint32_t  queued_at;// Timestamp at which this data buffer was queued
+      uint32_t  written_at; // Timestamp at which this data buffer was completely written
+      int       write_errno;  // If != 0, errno value while writing this buffer
       bool      owned;    // If true, we malloc'ed the data and should be freed after completely written.
                           // If false, app owns the memory and should ensure it remains valid until acked
     } queued_writebuf;
@@ -189,11 +197,8 @@ class AsyncClient : public AsyncSocketBase
 
     void _error(int8_t err);
     void _close(void);
-    bool _sockIsWriteable(void);
-    void _sockIsReadable(void);
-    void _sockPoll(void);
-    void _sockDelayedConnect(void);
     void _removeAllCallbacks(void);
+    bool _flushWriteQueue(void);
     void _clearWriteQueue(void);
 
     friend void _tcpsock_dns_found(const char * name, struct ip_addr * ipaddr, void * arg);