diff --git a/code/modules/power/apc.dm b/code/modules/power/apc.dm
index 7a5f17eeca..a98eb6a197 100644
--- a/code/modules/power/apc.dm
+++ b/code/modules/power/apc.dm
@@ -27,6 +27,7 @@
 #define APC_UPOVERLAY_ENVIRON1 1024
 #define APC_UPOVERLAY_ENVIRON2 2048
 #define APC_UPOVERLAY_LOCKED 4096
+#define APC_UPOVERLAY_OPERATING 8192
 
 #define APC_UPDATE_ICON_COOLDOWN 100 // 10 seconds
 
@@ -323,6 +324,9 @@
 	if(update_state <= 1)
 		update_state |= UPSTATE_ALLGOOD
 
+	if(operating)
+		update_overlay |= APC_UPOVERLAY_OPERATING
+
 	if(update_state & UPSTATE_ALLGOOD)
 		if(locked)
 			update_overlay |= APC_UPOVERLAY_LOCKED