diff --git a/src/modbus-rtu.c b/src/modbus-rtu.c
index 01e703d46..df3887dcb 100644
--- a/src/modbus-rtu.c
+++ b/src/modbus-rtu.c
@@ -91,8 +91,10 @@ static const uint8_t table_crc_lo[] = {
  * internal slave ID in slave mode */
 static int _modbus_set_slave(modbus_t *ctx, int slave)
 {
+    /* limt slave modified: 247 --> 255 */
+    int max_slave = 255;
     /* Broadcast address is 0 (MODBUS_BROADCAST_ADDRESS) */
-    if (slave >= 0 && slave <= 247) {
+    if (slave >= 0 && slave <= max_slave) {
         ctx->slave = slave;
     } else {
         errno = EINVAL;
diff --git a/src/modbus-udp.c b/src/modbus-udp.c
index 768814883..ee58ec2ff 100644
--- a/src/modbus-udp.c
+++ b/src/modbus-udp.c
@@ -183,6 +183,8 @@ static ssize_t _modbus_udp_recv(modbus_t *ctx, uint8_t *rsp, int rsp_length) {
 		int len = ctx_udp->_u > rsp_length ? rsp_length : ctx_udp->_u;
 		memcpy(rsp, ctx_udp->buffer, (size_t) len);
 		ctx_udp->_u -= len;
+        // Shift the buffer.
+        memmove(ctx_udp->buffer,ctx_udp->buffer+len,(size_t)ctx_udp->_u);
 		return len;
 	} else {
 		if( rsp_length > MODBUS_UDP_MAX_ADU_LENGTH )