diff --git a/timer.c b/timer.c
index f881ab3..2a555d7 100644
--- a/timer.c
+++ b/timer.c
@@ -77,7 +77,9 @@ ISR(TIMER1_COMPA_vect) {
 	// Check if this is a real step, or just a next_step_time "overflow"
 	if (next_step_time < 65536) {
 		// step!
-		WRITE(SCK, 1);
+		#ifdef DEBUG_LED_PIN
+			WRITE(DEBUG_LED_PIN, 1);
+		#endif
 
 		// disable this interrupt. if we set a new timeout, it will be re-enabled when appropriate
 		TIMSK1 &= ~MASK(OCIE1A);
@@ -87,7 +89,9 @@ ISR(TIMER1_COMPA_vect) {
 		queue_step();
 
 		// led off
-		WRITE(SCK, 0);
+		#ifdef DEBUG_LED_PIN
+			WRITE(DEBUG_LED_PIN, 0);
+		#endif
 		
 		// Enable the timer1_compa interrupt, if needed, 
 		// but only do it after disabling global interrupts.