diff --git a/freemodbus/modbus/ascii/mbascii_m.c b/freemodbus/modbus/ascii/mbascii_m.c
index 849ab65..a883a23 100644
--- a/freemodbus/modbus/ascii/mbascii_m.c
+++ b/freemodbus/modbus/ascii/mbascii_m.c
@@ -437,7 +437,8 @@ xMBMasterASCIITransmitFSM( void )
         /* Notify the task which called eMBMasterASCIISend that the frame has
          * been sent. */
     case STATE_M_TX_NOTIFY:
-        xFrameIsBroadcast = ( ucMasterASCIISndBuf[MB_SER_PDU_ADDR_OFF] == MB_ADDRESS_BROADCAST ) ? TRUE : FALSE;
+        xFrameIsBroadcast = ( ucMasterASCIISndBuf[MB_SEND_BUF_PDU_OFF - MB_SER_PDU_PDU_OFF] 
+                                                    == MB_ADDRESS_BROADCAST ) ? TRUE : FALSE;
         vMBMasterRequestSetType( xFrameIsBroadcast );
         eSndState = STATE_M_TX_XFWR;
         /* If the frame is broadcast ,master will enable timer of convert delay,
diff --git a/freemodbus/modbus/rtu/mbrtu_m.c b/freemodbus/modbus/rtu/mbrtu_m.c
index 65ac4b7..863b569 100644
--- a/freemodbus/modbus/rtu/mbrtu_m.c
+++ b/freemodbus/modbus/rtu/mbrtu_m.c
@@ -350,7 +350,8 @@ xMBMasterRTUTransmitFSM( void )
         }
         else
         {
-            xFrameIsBroadcast = ( ucMasterRTUSndBuf[MB_SER_PDU_ADDR_OFF] == MB_ADDRESS_BROADCAST ) ? TRUE : FALSE;
+            xFrameIsBroadcast = ( ucMasterRTUSndBuf[MB_SEND_BUF_PDU_OFF - MB_SER_PDU_PDU_OFF]
+                                                        == MB_ADDRESS_BROADCAST ) ? TRUE : FALSE;
             vMBMasterRequestSetType( xFrameIsBroadcast );
             eSndState = STATE_M_TX_XFWR;
             /* If the frame is broadcast ,master will enable timer of convert delay,