diff --git a/temp.c b/temp.c
index 8023b8f..22ca721 100644
--- a/temp.c
+++ b/temp.c
@@ -228,7 +228,7 @@ void temp_sensor_tick() {
 				all_within_range = 0;
 			}
 			
-			if (temp_sensors[i].heater_index != 255) {
+			if (temp_sensors[i].heater_index < NUM_HEATERS) {
 				heater_tick(temp_sensors[i].heater_index, temp_sensors_runtime[i].last_read_temp, temp_sensors_runtime[i].target_temp);
 			}
 		}