diff --git a/lib/include/mqtt_msg.h b/lib/include/mqtt_msg.h
index f91dffd..a7b070c 100644
--- a/lib/include/mqtt_msg.h
+++ b/lib/include/mqtt_msg.h
@@ -63,9 +63,9 @@ enum mqtt_message_type {
 
 typedef struct mqtt_message {
     uint8_t *data;
-    uint32_t length;
-    uint32_t fragmented_msg_total_length;       /*!< total len of fragmented messages (zero for all other messages) */
-    uint32_t fragmented_msg_data_offset;        /*!< data offset of fragmented messages (zero for all other messages) */
+    size_t length;
+    size_t fragmented_msg_total_length;       /*!< total len of fragmented messages (zero for all other messages) */
+    size_t fragmented_msg_data_offset;        /*!< data offset of fragmented messages (zero for all other messages) */
 } mqtt_message_t;
 
 typedef struct mqtt_connection {
@@ -73,7 +73,7 @@ typedef struct mqtt_connection {
 
     uint16_t message_id;
     uint8_t *buffer;
-    uint32_t buffer_length;
+    size_t buffer_length;
 
 } mqtt_connection_t;
 
@@ -122,13 +122,13 @@ static inline int mqtt_get_retain(const uint8_t *buffer)
     return (buffer[0] & 0x01);
 }
 
-void mqtt_msg_init(mqtt_connection_t *connection, uint8_t *buffer, uint32_t buffer_length);
-bool mqtt_header_complete(uint8_t *buffer, uint32_t buffer_length);
-uint32_t mqtt_get_total_length(const uint8_t *buffer, uint32_t length, int *fixed_size_len);
-char *mqtt_get_publish_topic(uint8_t *buffer, uint32_t *length);
-char *mqtt_get_publish_data(uint8_t *buffer, uint32_t *length);
-uint16_t mqtt_get_id(uint8_t *buffer, uint32_t length);
-int mqtt_has_valid_msg_hdr(uint8_t *buffer, uint32_t length);
+void mqtt_msg_init(mqtt_connection_t *connection, uint8_t *buffer, size_t buffer_length);
+bool mqtt_header_complete(uint8_t *buffer, size_t buffer_length);
+size_t mqtt_get_total_length(const uint8_t *buffer, size_t length, int *fixed_size_len);
+char *mqtt_get_publish_topic(uint8_t *buffer, size_t *length);
+char *mqtt_get_publish_data(uint8_t *buffer, size_t *length);
+uint16_t mqtt_get_id(uint8_t *buffer, size_t length);
+int mqtt_has_valid_msg_hdr(uint8_t *buffer, size_t length);
 
 mqtt_message_t *mqtt_msg_connect(mqtt_connection_t *connection, mqtt_connect_info_t *info);
 mqtt_message_t *mqtt_msg_publish(mqtt_connection_t *connection, const char *topic, const char *data, int data_length, int qos, int retain, uint16_t *message_id);
diff --git a/lib/mqtt_msg.c b/lib/mqtt_msg.c
index f6f983e..fcfe538 100644
--- a/lib/mqtt_msg.c
+++ b/lib/mqtt_msg.c
@@ -133,17 +133,17 @@ static mqtt_message_t *fini_message(mqtt_connection_t *connection, int type, int
     return &connection->message;
 }
 
-void mqtt_msg_init(mqtt_connection_t *connection, uint8_t *buffer, uint32_t buffer_length)
+void mqtt_msg_init(mqtt_connection_t *connection, uint8_t *buffer, size_t buffer_length)
 {
     memset(connection, 0, sizeof(mqtt_connection_t));
     connection->buffer = buffer;
     connection->buffer_length = buffer_length;
 }
 
-uint32_t mqtt_get_total_length(const uint8_t *buffer, uint32_t length, int *fixed_size_len)
+size_t mqtt_get_total_length(const uint8_t *buffer, size_t length, int *fixed_size_len)
 {
     int i;
-    uint32_t totlen = 0;
+    size_t totlen = 0;
 
     for (i = 1; i < length; ++i) {
         totlen += (buffer[i] & 0x7f) << (7 * (i - 1));
@@ -160,7 +160,7 @@ uint32_t mqtt_get_total_length(const uint8_t *buffer, uint32_t length, int *fixe
     return totlen;
 }
 
-bool mqtt_header_complete(uint8_t *buffer, uint32_t buffer_length)
+bool mqtt_header_complete(uint8_t *buffer, size_t buffer_length)
 {
     uint16_t i;
     uint16_t topiclen;
@@ -191,7 +191,7 @@ bool mqtt_header_complete(uint8_t *buffer, uint32_t buffer_length)
     return buffer_length >= i;
 }
 
-char *mqtt_get_publish_topic(uint8_t *buffer, uint32_t *length)
+char *mqtt_get_publish_topic(uint8_t *buffer, size_t *length)
 {
     int i;
     int totlen = 0;
@@ -220,7 +220,7 @@ char *mqtt_get_publish_topic(uint8_t *buffer, uint32_t *length)
     return (char *)(buffer + i);
 }
 
-char *mqtt_get_publish_data(uint8_t *buffer, uint32_t *length)
+char *mqtt_get_publish_data(uint8_t *buffer, size_t *length)
 {
     int i;
     int totlen = 0;
@@ -268,7 +268,7 @@ char *mqtt_get_publish_data(uint8_t *buffer, uint32_t *length)
     return (char *)(buffer + i);
 }
 
-uint16_t mqtt_get_id(uint8_t *buffer, uint32_t length)
+uint16_t mqtt_get_id(uint8_t *buffer, size_t length)
 {
     if (length < 1) {
         return 0;
@@ -558,7 +558,7 @@ mqtt_message_t *mqtt_msg_disconnect(mqtt_connection_t *connection)
  * check flags: [MQTT-2.2.2-1], [MQTT-2.2.2-2]
  * returns 0 if flags are invalid, otherwise returns 1
  */
-int mqtt_has_valid_msg_hdr(uint8_t *buffer, uint32_t length)
+int mqtt_has_valid_msg_hdr(uint8_t *buffer, size_t length)
 {
     int qos, dup;
 
diff --git a/mqtt_client.c b/mqtt_client.c
index aff0809..6f9b30a 100644
--- a/mqtt_client.c
+++ b/mqtt_client.c
@@ -43,8 +43,8 @@ typedef struct mqtt_state
     uint8_t *out_buffer;
     int in_buffer_length;
     int out_buffer_length;
-    uint32_t message_length;
-    uint32_t in_buffer_read_len;
+    size_t message_length;
+    size_t in_buffer_read_len;
     mqtt_message_t *outbound_message;
     mqtt_connection_t mqtt_connection;
     uint16_t pending_msg_id;