diff --git a/components/net/freemodbus/modbus/rtu/mbrtu.c b/components/net/freemodbus/modbus/rtu/mbrtu.c
index c023c92654..ae5e0325c1 100644
--- a/components/net/freemodbus/modbus/rtu/mbrtu.c
+++ b/components/net/freemodbus/modbus/rtu/mbrtu.c
@@ -153,7 +153,7 @@ eMBRTUReceive( UCHAR * pucRcvAddress, UCHAR ** pucFrame, USHORT * pusLength )
     eMBErrorCode    eStatus = MB_ENOERR;
 
     ENTER_CRITICAL_SECTION(  );
-    assert_param( usRcvBufferPos < MB_SER_PDU_SIZE_MAX );
+    assert_param( usRcvBufferPos <= MB_SER_PDU_SIZE_MAX );
 
     /* Length and CRC check */
     if( ( usRcvBufferPos >= MB_SER_PDU_SIZE_MIN )