diff --git a/mote/v2/avr/debug.h b/mote/v2/avr/debug.h
index 98d8a12..1e23d73 100644
--- a/mote/v2/avr/debug.h
+++ b/mote/v2/avr/debug.h
@@ -1,14 +1,20 @@
 #if DBG > 0
 	/* set LED pin high/low at the start/end of an ISR */
-	#define DBG_ISR_BEGIN	PORTB |= (1<<PB0);
-	#define DBG_ISR_END	PORTB &= ~(1<<PB0);
+	#define DBG_ISR_BEGIN()		PORTB |= (1<<PB0)
+	#define DBG_ISR_END()		PORTB &= ~(1<<PB0)
 
 	/* Set PB1=OC1A as output pin and toggle this pin on TIMER1 compare match */
-	#define  DBG_OC1A_TOGGLE	DDRB |= (1<<DDB1); \
-					TCCR1A |= 1<<COM1A0;
-#else
-	#define DBG_ISR_BEGIN	/* nothing */
-	#define DBG_ISR_END	/* nothing */
-	#define DBG_OC1A_TOGGLE	/* nothing */
-#endif
+	#define  DBG_OC1A_TOGGLE()	DDRB |= (1<<DDB1); \
+					TCCR1A |= 1<<COM1A0
 
+	#define DBG_LED_ON()		/* nothing */
+	#define DBG_LED_OFF()		/* nothing */
+#else
+	#define DBG_ISR_BEGIN()		/* nothing */
+	#define DBG_ISR_END()		/* nothing */
+	#define DBG_OC1A_TOGGLE()	/* nothing */
+
+	/* LED behaviour in non-debugging mode */
+	#define DBG_LED_ON()		PORTB &= ~(1<<PB0)
+	#define DBG_LED_OFF()		PORTB |= (1<<PB0)
+#endif
diff --git a/mote/v2/avr/main.c b/mote/v2/avr/main.c
index dffeaae..e9f8fef 100644
--- a/mote/v2/avr/main.c
+++ b/mote/v2/avr/main.c
@@ -63,11 +63,12 @@ ISR(SPI_STC_vect)
 	uint8_t spi_rx, rx, tx; 
 	uint16_t spi_tx;
 
-	DBG_ISR_BEGIN
+	DBG_ISR_BEGIN();
 
 	// the SPI is double-buffered, requiring two NO_OPs when switching from Tx to Rx
 	if (spi_status & (SPI_NO_OP_1 | SPI_NO_OP_2)) {
 		spi_status--;
+		DBG_LED_ON();
 		return;
 	}
 
@@ -127,9 +128,11 @@ ISR(SPI_STC_vect)
 			break;
 		case SPI_FORWARD_TO_UART_PORT:
 			spi_status |= SPI_TO_FROM_UART;
+			DBG_LED_OFF();
 			break;
 		case SPI_FORWARD_TO_CTRL_PORT:
 			spi_status &= ~SPI_TO_FROM_UART;
+			DBG_LED_OFF();
 			break;
 		default:
 			if (spi_status & SPI_HIGH_HEX) {
@@ -150,7 +153,7 @@ ISR(SPI_STC_vect)
 			spi_status ^= SPI_HIGH_HEX;
 	}
 
-        DBG_ISR_END
+        DBG_ISR_END();
 }
 
 ISR(INT0_vect)
@@ -178,7 +181,7 @@ ISR(TIMER1_COMPA_vect)
 {
 	uint8_t muxn_l = phy_to_log[muxn];
 	
-	DBG_ISR_BEGIN
+	DBG_ISR_BEGIN();
 
 	MacU16X16to32(state[muxn_l].nano, sensor[muxn_l].meterconst, ADC);
 
@@ -212,7 +215,7 @@ ISR(TIMER1_COMPA_vect)
 	/* Start a new ADC conversion. */
 	ADCSRA |= (1<<ADSC);
 
-	DBG_ISR_END
+	DBG_ISR_END();
 }
 
 ISR(ANALOG_COMP_vect)
@@ -287,7 +290,7 @@ void setup_timer1(void)
 	// Enable output compare match interrupt for timer1 (DS p.136)
 	TIMSK1 |= (1<<OCIE1A);
 
-	DBG_OC1A_TOGGLE
+	DBG_OC1A_TOGGLE();
 }
 
 void setup_analog_comparator(void)