diff --git a/usart/main.cpp b/usart/main.cpp
index 520ef4b..4b47263 100644
--- a/usart/main.cpp
+++ b/usart/main.cpp
@@ -11,6 +11,7 @@
 
 int main()
 {
+	sei();
 	USART0 &cUSART = USART0::inst();
 	cUSART.init();
 
diff --git a/usart/usart.cpp b/usart/usart.cpp
index 52a0a5a..1f4c025 100644
--- a/usart/usart.cpp
+++ b/usart/usart.cpp
@@ -252,16 +252,21 @@ void USART0::init( uint32_t ui32BaudRate /* = 9600 */, uint8_t ui8DataBits /* =
 
 	setRXState( true );
 	setTXState( true );
+
 	setRXInterrupt( true );
 	setUDREInterrupt( false );
-
-	sei();
 }
 
 //////////////////////////////////////////////////////////////////////////
 bool USART0::receiveByte( uint8_t &ui8Data )
 {
-	if( m_vsizeRXBufferHead == m_vsizeRXBufferTail )
+	if( m_vsizeRXBufferHead == m_vsizeRXBufferTail && !( SREG & ( 1 << SREG_I ) ) )
+	{
+		while( !( *m_vui8pUCSRA & ( 1 << RXC_D ) ) );
+		ui8Data = *m_vui8pUDR;
+		return true;
+	}
+	else if( m_vsizeRXBufferHead == m_vsizeRXBufferTail )
 	{
 		return false;
 	}
@@ -291,11 +296,11 @@ bool USART0::receiveByte( uint8_t &ui8Data, uint16_t ui16DelayMS )
 }
 
 //////////////////////////////////////////////////////////////////////////
-bool USART0::receiveLine( char *szBuffer, size_t sizeBufferLength, const char *szLineTerminator /* = "\r\n" */, size_t sizeMaxSize /* = 512 */ )
+bool USART0::receiveLine( char *szBuffer, size_t sizeBufferLength, const char *szLineTerminator /* = "\r\n" */ )
 {
 	size_t sizeReceived = 0;
 
-	while( sizeReceived < sizeMaxSize - 1 && sizeReceived < sizeBufferLength - 1 )
+	while( sizeReceived < sizeBufferLength - 1 )
 	{
 		uint8_t ui8ReceiveByte;
 
@@ -323,12 +328,26 @@ void USART0::transmitByte( uint8_t ui8Data )
 
 	size_t sizeIndex = ( m_vsizeTXBufferHead + 1 ) % sm_sizeTXBUFFER_SIZE;
 
-	while( sizeIndex == m_vsizeTXBufferTail );
+	while( sizeIndex == m_vsizeTXBufferTail )
+	{
+		if( !( SREG & ( 1 << SREG_I ) ) && *m_vui8pUCSRA & ( 1 << UDRE_D ) )
+		{
+			transmitInterruptHandler();
+		}
+	}
 
 	m_vui8aTXBuffer[m_vsizeTXBufferHead] = ui8Data;
 	m_vsizeTXBufferHead = sizeIndex;
 
-	setUDREInterrupt( true );
+	if( !( SREG & ( 1 << SREG_I ) ) )
+	{
+		while( !( *m_vui8pUCSRA & ( 1 << UDRE_D ) ) );
+		transmitInterruptHandler();
+	}
+	else
+	{
+		setUDREInterrupt( true );
+	}
 }
 
 //////////////////////////////////////////////////////////////////////////
diff --git a/usart/usart.h b/usart/usart.h
index 8cd3d88..c282bfa 100644
--- a/usart/usart.h
+++ b/usart/usart.h
@@ -137,7 +137,7 @@ public:
 
 	bool receiveByte( uint8_t &ui8Data );
 	bool receiveByte( uint8_t &ui8Data, uint16_t ui16DelayMS );
-	bool receiveLine( char *szBuffer, size_t sizeBufferLength, const char *szLineTerminator = "\r\n", size_t sizeMaxSize = 512 );
+	bool receiveLine( char *szBuffer, size_t sizeBufferLength, const char *szLineTerminator = "\r\n" );
 
 	void transmitByte( uint8_t ui8Data );
 	void transmitString( const char *szString );