diff --git a/examples/mqtt-over-ws-client/main.c b/examples/mqtt-over-ws-client/main.c
index 62f4f511..d1cd88c7 100644
--- a/examples/mqtt-over-ws-client/main.c
+++ b/examples/mqtt-over-ws-client/main.c
@@ -7,7 +7,7 @@
 //    3. Publishes message `hello` to the `s_topic`
 //    4. Receives that message back from the subscribed topic and exits
 //
-// To enable SSL/TLS, make SSL=OPENSSL or make SSL=MBEDTLS 
+// To enable SSL/TLS, make SSL=OPENSSL or make SSL=MBEDTLS
 
 #include "mongoose.h"
 
@@ -33,10 +33,11 @@ static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
     size_t len = c->send.len;
     mg_mqtt_login(c, &opts);
     mg_ws_wrap(c, c->send.len - len, WEBSOCKET_OP_BINARY);
+    c->is_hexdumping = 1;
   } else if (ev == MG_EV_WS_MSG) {
     struct mg_mqtt_message mm;
     struct mg_ws_message *wm = (struct mg_ws_message *) ev_data;
-    uint8_t version = (uint8_t) (size_t) c->pfn_data;
+    uint8_t version = c->is_mqtt5 ? 5 : 4;
     MG_INFO(("GOT %d bytes WS msg", (int) wm->data.len));
     while ((mg_mqtt_parse((uint8_t *) wm->data.ptr, wm->data.len, version,
                           &mm)) == 0) {
@@ -82,6 +83,7 @@ int main(void) {
   struct mg_mgr mgr;  // Event manager
   bool done = false;  // Event handler flips it to true when done
   mg_mgr_init(&mgr);  // Initialise event manager
+  mg_log_set("4");    // Set debug log level
   mg_ws_connect(&mgr, s_url, fn, &done, NULL);    // Create client connection
   while (done == false) mg_mgr_poll(&mgr, 1000);  // Event loop
   mg_mgr_free(&mgr);                              // Finished, cleanup
diff --git a/mongoose.c b/mongoose.c
index adee0e4c..cca3e8c3 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -3035,7 +3035,7 @@ void mg_mqtt_login(struct mg_connection *c, const struct mg_mqtt_opts *opts) {
   }
 
   if (hdr[6] == 0) hdr[6] = 4;  // If version is not set, use 4 (3.1.1)
-  c->pfn_data = (void *) (size_t) hdr[6];          // Store version
+  c->is_mqtt5 = hdr[6] == 5;    // Set version 5 flag
   hdr[7] = (uint8_t) ((opts->will_qos & 3) << 3);  // Connection flags
   if (opts->user.len > 0) {
     total_len += 2 + (uint32_t) opts->user.len;
@@ -3053,19 +3053,19 @@ void mg_mqtt_login(struct mg_connection *c, const struct mg_mqtt_opts *opts) {
   if (opts->clean || cid.len == 0) hdr[7] |= MQTT_CLEAN_SESSION;
   if (opts->will_retain) hdr[7] |= MQTT_WILL_RETAIN;
   total_len += (uint32_t) cid.len;
-  if (opts->version == 5) total_len += 1U + (hdr[7] & MQTT_HAS_WILL ? 1U : 0);
+  if (c->is_mqtt5) total_len += 1U + (hdr[7] & MQTT_HAS_WILL ? 1U : 0);
 
   mg_mqtt_send_header(c, MQTT_CMD_CONNECT, 0, total_len);
   mg_send(c, hdr, sizeof(hdr));
   // keepalive == 0 means "do not disconnect us!"
   mg_send_u16(c, mg_htons((uint16_t) opts->keepalive));
 
-  if (opts->version == 5) mg_send(c, &zero, sizeof(zero));  // V5 properties
+  if (c->is_mqtt5) mg_send(c, &zero, sizeof(zero));  // V5 properties
   mg_send_u16(c, mg_htons((uint16_t) cid.len));
   mg_send(c, cid.ptr, cid.len);
 
   if (hdr[7] & MQTT_HAS_WILL) {
-    if (opts->version == 5) mg_send(c, &zero, sizeof(zero));  // will props
+    if (c->is_mqtt5) mg_send(c, &zero, sizeof(zero));  // will props
     mg_send_u16(c, mg_htons((uint16_t) opts->will_topic.len));
     mg_send(c, opts->will_topic.ptr, opts->will_topic.len);
     mg_send_u16(c, mg_htons((uint16_t) opts->will_message.len));
@@ -3083,13 +3083,12 @@ void mg_mqtt_login(struct mg_connection *c, const struct mg_mqtt_opts *opts) {
 
 void mg_mqtt_pub(struct mg_connection *c, struct mg_str topic,
                  struct mg_str data, int qos, bool retain) {
-  uint8_t flags = (uint8_t) (((qos & 3) << 1) | (retain ? 1 : 0));
-  uint8_t version = (uint8_t) (size_t) c->pfn_data, zero = 0;
+  uint8_t flags = (uint8_t) (((qos & 3) << 1) | (retain ? 1 : 0)), zero = 0;
   uint32_t len = 2 + (uint32_t) topic.len + (uint32_t) data.len;
   MG_DEBUG(("%lu [%.*s] -> [%.*s]", c->id, (int) topic.len, (char *) topic.ptr,
             (int) data.len, (char *) data.ptr));
   if (qos > 0) len += 2;
-  if (version == 5) len++;
+  if (c->is_mqtt5) len++;
   mg_mqtt_send_header(c, MQTT_CMD_PUBLISH, flags, len);
   mg_send_u16(c, mg_htons((uint16_t) topic.len));
   mg_send(c, topic.ptr, topic.len);
@@ -3097,17 +3096,17 @@ void mg_mqtt_pub(struct mg_connection *c, struct mg_str topic,
     if (++c->mgr->mqtt_id == 0) ++c->mgr->mqtt_id;
     mg_send_u16(c, mg_htons(c->mgr->mqtt_id));
   }
-  if (version == 5) mg_send(c, &zero, sizeof(zero));
+  if (c->is_mqtt5) mg_send(c, &zero, sizeof(zero));
   mg_send(c, data.ptr, data.len);
 }
 
 void mg_mqtt_sub(struct mg_connection *c, struct mg_str topic, int qos) {
-  uint8_t qos_ = qos & 3, version = (uint8_t) (size_t) c->pfn_data, zero = 0;
-  uint32_t len = 2 + (uint32_t) topic.len + 2 + 1 + (version == 5 ? 1 : 0);
+  uint8_t qos_ = qos & 3, zero = 0;
+  uint32_t len = 2 + (uint32_t) topic.len + 2 + 1 + (c->is_mqtt5 ? 1 : 0);
   mg_mqtt_send_header(c, MQTT_CMD_SUBSCRIBE, 2, len);
   if (++c->mgr->mqtt_id == 0) ++c->mgr->mqtt_id;
   mg_send_u16(c, mg_htons(c->mgr->mqtt_id));
-  if (version == 5) mg_send(c, &zero, sizeof(zero));
+  if (c->is_mqtt5) mg_send(c, &zero, sizeof(zero));
   mg_send_u16(c, mg_htons((uint16_t) topic.len));
   mg_send(c, topic.ptr, topic.len);
   mg_send(c, &qos_, sizeof(qos_));
@@ -3208,7 +3207,7 @@ static void mqtt_cb(struct mg_connection *c, int ev, void *ev_data,
                     void *fn_data) {
   if (ev == MG_EV_READ) {
     for (;;) {
-      uint8_t version = (uint8_t) (size_t) c->pfn_data;
+      uint8_t version = c->is_mqtt5 ? 5 : 4;
       struct mg_mqtt_message mm;
       int rc = mg_mqtt_parse(c->recv.buf, c->recv.len, version, &mm);
       if (rc == MQTT_MALFORMED) {
diff --git a/mongoose.h b/mongoose.h
index 959b6288..b8d6b5bc 100644
--- a/mongoose.h
+++ b/mongoose.h
@@ -1036,6 +1036,7 @@ struct mg_connection {
   unsigned is_tls_hs : 1;      // TLS handshake is in progress
   unsigned is_udp : 1;         // UDP connection
   unsigned is_websocket : 1;   // WebSocket connection
+  unsigned is_mqtt5 : 1;       // For MQTT connection, v5 indicator
   unsigned is_hexdumping : 1;  // Hexdump in/out traffic
   unsigned is_draining : 1;    // Send remaining data, then close and free
   unsigned is_closing : 1;     // Close and free the connection immediately
diff --git a/src/mqtt.c b/src/mqtt.c
index d3d9aae2..4daa3bc4 100644
--- a/src/mqtt.c
+++ b/src/mqtt.c
@@ -43,7 +43,7 @@ void mg_mqtt_login(struct mg_connection *c, const struct mg_mqtt_opts *opts) {
   }
 
   if (hdr[6] == 0) hdr[6] = 4;  // If version is not set, use 4 (3.1.1)
-  c->pfn_data = (void *) (size_t) hdr[6];          // Store version
+  c->is_mqtt5 = hdr[6] == 5;    // Set version 5 flag
   hdr[7] = (uint8_t) ((opts->will_qos & 3) << 3);  // Connection flags
   if (opts->user.len > 0) {
     total_len += 2 + (uint32_t) opts->user.len;
@@ -61,19 +61,19 @@ void mg_mqtt_login(struct mg_connection *c, const struct mg_mqtt_opts *opts) {
   if (opts->clean || cid.len == 0) hdr[7] |= MQTT_CLEAN_SESSION;
   if (opts->will_retain) hdr[7] |= MQTT_WILL_RETAIN;
   total_len += (uint32_t) cid.len;
-  if (opts->version == 5) total_len += 1U + (hdr[7] & MQTT_HAS_WILL ? 1U : 0);
+  if (c->is_mqtt5) total_len += 1U + (hdr[7] & MQTT_HAS_WILL ? 1U : 0);
 
   mg_mqtt_send_header(c, MQTT_CMD_CONNECT, 0, total_len);
   mg_send(c, hdr, sizeof(hdr));
   // keepalive == 0 means "do not disconnect us!"
   mg_send_u16(c, mg_htons((uint16_t) opts->keepalive));
 
-  if (opts->version == 5) mg_send(c, &zero, sizeof(zero));  // V5 properties
+  if (c->is_mqtt5) mg_send(c, &zero, sizeof(zero));  // V5 properties
   mg_send_u16(c, mg_htons((uint16_t) cid.len));
   mg_send(c, cid.ptr, cid.len);
 
   if (hdr[7] & MQTT_HAS_WILL) {
-    if (opts->version == 5) mg_send(c, &zero, sizeof(zero));  // will props
+    if (c->is_mqtt5) mg_send(c, &zero, sizeof(zero));  // will props
     mg_send_u16(c, mg_htons((uint16_t) opts->will_topic.len));
     mg_send(c, opts->will_topic.ptr, opts->will_topic.len);
     mg_send_u16(c, mg_htons((uint16_t) opts->will_message.len));
@@ -91,13 +91,12 @@ void mg_mqtt_login(struct mg_connection *c, const struct mg_mqtt_opts *opts) {
 
 void mg_mqtt_pub(struct mg_connection *c, struct mg_str topic,
                  struct mg_str data, int qos, bool retain) {
-  uint8_t flags = (uint8_t) (((qos & 3) << 1) | (retain ? 1 : 0));
-  uint8_t version = (uint8_t) (size_t) c->pfn_data, zero = 0;
+  uint8_t flags = (uint8_t) (((qos & 3) << 1) | (retain ? 1 : 0)), zero = 0;
   uint32_t len = 2 + (uint32_t) topic.len + (uint32_t) data.len;
   MG_DEBUG(("%lu [%.*s] -> [%.*s]", c->id, (int) topic.len, (char *) topic.ptr,
             (int) data.len, (char *) data.ptr));
   if (qos > 0) len += 2;
-  if (version == 5) len++;
+  if (c->is_mqtt5) len++;
   mg_mqtt_send_header(c, MQTT_CMD_PUBLISH, flags, len);
   mg_send_u16(c, mg_htons((uint16_t) topic.len));
   mg_send(c, topic.ptr, topic.len);
@@ -105,17 +104,17 @@ void mg_mqtt_pub(struct mg_connection *c, struct mg_str topic,
     if (++c->mgr->mqtt_id == 0) ++c->mgr->mqtt_id;
     mg_send_u16(c, mg_htons(c->mgr->mqtt_id));
   }
-  if (version == 5) mg_send(c, &zero, sizeof(zero));
+  if (c->is_mqtt5) mg_send(c, &zero, sizeof(zero));
   mg_send(c, data.ptr, data.len);
 }
 
 void mg_mqtt_sub(struct mg_connection *c, struct mg_str topic, int qos) {
-  uint8_t qos_ = qos & 3, version = (uint8_t) (size_t) c->pfn_data, zero = 0;
-  uint32_t len = 2 + (uint32_t) topic.len + 2 + 1 + (version == 5 ? 1 : 0);
+  uint8_t qos_ = qos & 3, zero = 0;
+  uint32_t len = 2 + (uint32_t) topic.len + 2 + 1 + (c->is_mqtt5 ? 1 : 0);
   mg_mqtt_send_header(c, MQTT_CMD_SUBSCRIBE, 2, len);
   if (++c->mgr->mqtt_id == 0) ++c->mgr->mqtt_id;
   mg_send_u16(c, mg_htons(c->mgr->mqtt_id));
-  if (version == 5) mg_send(c, &zero, sizeof(zero));
+  if (c->is_mqtt5) mg_send(c, &zero, sizeof(zero));
   mg_send_u16(c, mg_htons((uint16_t) topic.len));
   mg_send(c, topic.ptr, topic.len);
   mg_send(c, &qos_, sizeof(qos_));
@@ -216,7 +215,7 @@ static void mqtt_cb(struct mg_connection *c, int ev, void *ev_data,
                     void *fn_data) {
   if (ev == MG_EV_READ) {
     for (;;) {
-      uint8_t version = (uint8_t) (size_t) c->pfn_data;
+      uint8_t version = c->is_mqtt5 ? 5 : 4;
       struct mg_mqtt_message mm;
       int rc = mg_mqtt_parse(c->recv.buf, c->recv.len, version, &mm);
       if (rc == MQTT_MALFORMED) {
diff --git a/src/net.h b/src/net.h
index f6c17083..b0cb80eb 100644
--- a/src/net.h
+++ b/src/net.h
@@ -60,6 +60,7 @@ struct mg_connection {
   unsigned is_tls_hs : 1;      // TLS handshake is in progress
   unsigned is_udp : 1;         // UDP connection
   unsigned is_websocket : 1;   // WebSocket connection
+  unsigned is_mqtt5 : 1;       // For MQTT connection, v5 indicator
   unsigned is_hexdumping : 1;  // Hexdump in/out traffic
   unsigned is_draining : 1;    // Send remaining data, then close and free
   unsigned is_closing : 1;     // Close and free the connection immediately