# UNDF: UNDF-2026-000000376
--- a/src/main/java/net/minecraft/world/level/block/piston/PistonStructureResolver.java
+++ b/src/main/java/net/minecraft/world/level/block/piston/PistonStructureResolver.java
@@ -15,6 +15,7 @@ public class PistonStructureResolver {
     private final List<BlockPos> toPush = Lists.newArrayList();
+    private final Set<BlockPos> toPushSet = new HashSet<>();
     private final List<BlockPos> toDestroy = Lists.newArrayList();

@@ -42,8 +43,8 @@ public class PistonStructureResolver {
-                if (!this.toPush.contains(blockPos)) {
+                if (this.toPushSet.add(blockPos)) {
                     this.toPush.add(blockPos);
                 }