diff --git a/global.c b/global.c
index bd39b73..cfef145 100644
--- a/global.c
+++ b/global.c
@@ -164,12 +164,12 @@ inline void led_toggle(void)
 
 void sleep_us(uint32_t duration)
 {
-	if (duration <= 5) { // less than the setup time
-		for (volatile uint32_t nop = 0; nop < 5 * duration; nop++); // busy loop, approximate, hand tuned for 72 MHz system clock
+	if (duration <= 4) { // less than the setup time
+		for (volatile uint32_t nop = 0; nop < 5 * duration; nop++); // busy loop, approximate
 		return;
 	}
 
-	duration -= 5; // subtract setup time
+	duration -= 4; // subtract setup time
 	systick_counter_disable(); // disable SysTick to reconfigure it
 	if (!systick_set_frequency(1000000, rcc_ahb_frequency)) { // set SysTick frequency to microseconds
 		 while (true); // unhandled error