diff --git a/core/src/main/java/com/shatteredpixel/shatteredpixeldungeon/levels/PrisonBossLevel.java b/core/src/main/java/com/shatteredpixel/shatteredpixeldungeon/levels/PrisonBossLevel.java
index 98a5a0c69..b9322bdce 100644
--- a/core/src/main/java/com/shatteredpixel/shatteredpixeldungeon/levels/PrisonBossLevel.java
+++ b/core/src/main/java/com/shatteredpixel/shatteredpixeldungeon/levels/PrisonBossLevel.java
@@ -369,7 +369,7 @@ public class PrisonBossLevel extends Level {
 		addVisuals(); //this also resets existing visuals
 		traps.clear();
 
-		for (CustomTilemap t : customTiles){
+		for (CustomTilemap t : customTiles.toArray(new CustomTilemap[0])){
 			if (t instanceof FadingTraps){
 				((FadingTraps) t).remove();
 			}