diff --git a/subsys/net/lib/lwm2m/lwm2m_engine.c b/subsys/net/lib/lwm2m/lwm2m_engine.c
index bbf68d1..bf65c5e 100644
--- a/subsys/net/lib/lwm2m/lwm2m_engine.c
+++ b/subsys/net/lib/lwm2m/lwm2m_engine.c
@@ -110,7 +110,9 @@ static sys_slist_t engine_observer_list;
 /* TODO: figure out what's correct value */
 #define TIMEOUT_BLOCKWISE_TRANSFER K_SECONDS(30)

-#define GET_BLOCK_NUM(v) ((v) >> 4)
+#define GET_BLOCK_NUM(v)	((v) >> 4)
+#define GET_BLOCK_SIZE(v)	(((v) & 0x7))
+#define GET_MORE(v)		(!!((v) & 0x08))

 struct block_context {
 	struct zoap_block_context ctx;
@@ -548,6 +550,20 @@ int lwm2m_delete_obj_inst(u16_t obj_id, u16_t obj_inst_id)

 /* utility functions */

+static int get_option_int(const struct zoap_packet *zpkt, u8_t opt)
+{
+	struct zoap_option option = {};
+	u16_t count = 1;
+	int r;
+
+	r = zoap_find_options(zpkt, opt, &option, count);
+	if (r <= 0) {
+		return -ENOENT;
+	}
+
+	return zoap_option_value_to_int(&option);
+}
+
 static void engine_clear_context(struct lwm2m_engine_context *context)
 {
 	if (context->in) {
@@ -1625,11 +1641,12 @@ int lwm2m_write_handler(struct lwm2m_engine_obj_inst *obj_inst,
 	void *data_ptr = NULL;
 	size_t data_len = 0;
 	size_t len = 0;
+	size_t total_size = 0;
 	int ret = 0;
-	struct block_context *block_ctx = NULL;
 	u8_t tkl = 0;
 	const u8_t *token;
 	bool last_block = true;
+	struct block_context *block_ctx = NULL;

 	if (!obj_inst || !res || !obj_field || !context) {
 		return -EINVAL;
@@ -1639,6 +1656,13 @@ int lwm2m_write_handler(struct lwm2m_engine_obj_inst *obj_inst,
 	data_ptr = res->data_ptr;
 	data_len = res->data_len;

+	/* setup data_ptr/data_len for OPAQUE when it has none setup */
+	if (obj_field->data_type == LWM2M_RES_TYPE_OPAQUE &&
+	    data_ptr == NULL && data_len == 0) {
+		data_ptr = in->inbuf;
+		data_len = in->insize;
+	}
+
 	/* allow user to override data elements via callback */
 	if (res->pre_write_cb) {
 		data_ptr = res->pre_write_cb(obj_inst->obj_inst_id, &data_len);
@@ -1731,14 +1755,22 @@ int lwm2m_write_handler(struct lwm2m_engine_obj_inst *obj_inst,
 	}

 	if (res->post_write_cb) {
-		token = zoap_header_get_token(in->in_zpkt, &tkl);
-		if (token != NULL && !get_block_ctx(token, tkl, &block_ctx)) {
-			last_block = block_ctx->ctx.current == 0;
+		/* Get block1 option for checking MORE block flag */
+		ret = get_option_int(in->in_zpkt, ZOAP_OPTION_BLOCK1);
+		if (ret >= 0) {
+			last_block = !GET_MORE(ret);
+
+			/* Get block_ctx for total_size (might be zero) */
+			token = zoap_header_get_token(in->in_zpkt, &tkl);
+			if (token != NULL &&
+			    !get_block_ctx(token, tkl, &block_ctx)) {
+				total_size = block_ctx->ctx.total_size;
+			}
 		}

 		/* ignore return value here */
 		ret = res->post_write_cb(obj_inst->obj_inst_id, data_ptr, len,
-					 last_block, 0);
+					 last_block, total_size);
 		if (ret >= 0) {
 			ret = 0;
 		}
@@ -2054,20 +2086,6 @@ static int do_write_op(struct lwm2m_engine_obj *obj,
 	}
 }

-static int get_option_int(const struct zoap_packet *zpkt, u8_t opt)
-{
-	struct zoap_option option = {};
-	u16_t count = 1;
-	int r;
-
-	r = zoap_find_options(zpkt, opt, &option, count);
-	if (r <= 0) {
-		return -ENOENT;
-	}
-
-	return zoap_option_value_to_int(&option);
-}
-
 static int handle_request(struct zoap_packet *request,
 			  struct zoap_packet *response,
 			  struct sockaddr *from_addr)
@@ -2086,6 +2104,8 @@ static int handle_request(struct zoap_packet *request,
 	int observe = -1; /* default to -1, 0 = ENABLE, 1 = DISABLE */
 	bool discover = false;
 	struct block_context *block_ctx = NULL;
+	size_t block_offset = 0;
+	enum zoap_block_size block_size;

 	/* setup engine context */
 	memset(&context, 0, sizeof(struct lwm2m_engine_context));
@@ -2201,6 +2221,15 @@ static int handle_request(struct zoap_packet *request,
 	/* Check for block transfer */
 	r = get_option_int(in.in_zpkt, ZOAP_OPTION_BLOCK1);
 	if (r > 0) {
+		/* RFC7252: 4.6. Message Size */
+		block_size = GET_BLOCK_SIZE(r);
+		if (GET_MORE(r) &&
+		    zoap_block_size_to_bytes(block_size) > in.insize) {
+			SYS_LOG_DBG("Trailing payload is discarded!");
+			r = -EFBIG;
+			goto error;
+		}
+
 		if (GET_BLOCK_NUM(r) == 0) {
 			r = init_block_ctx(token, tkl, &block_ctx);
 		} else {
@@ -2211,7 +2240,8 @@ static int handle_request(struct zoap_packet *request,
 			goto error;
 		}

-		zoap_next_block(in.in_zpkt, &block_ctx->ctx);
+		/* 0 will be returned if it's the last block */
+		block_offset = zoap_next_block(in.in_zpkt, &block_ctx->ctx);
 	}

 	switch (context.operation) {
@@ -2289,7 +2319,7 @@ static int handle_request(struct zoap_packet *request,

 	/* Handle blockwise 1 */
 	if (block_ctx) {
-		if (block_ctx->ctx.current > 0) {
+		if (block_offset > 0) {
 			/* More to come, ack with correspond block # */
 			r = zoap_add_block1_option(
 					out.out_zpkt, &block_ctx->ctx);
@@ -2327,6 +2357,9 @@ error:
 	} else if (r == -EEXIST) {
 		zoap_header_set_code(out.out_zpkt,
 				     ZOAP_RESPONSE_CODE_BAD_REQUEST);
+	} else if (r == -EFBIG) {
+		zoap_header_set_code(out.out_zpkt,
+				     ZOAP_RESPONSE_CODE_REQUEST_TOO_LARGE);
 	} else {
 		/* Failed to handle the request */
 		zoap_header_set_code(out.out_zpkt,