diff --git a/BauSystem_Main/src/de/steamwar/bausystem/features/simulator/SimulatorCursor.java b/BauSystem_Main/src/de/steamwar/bausystem/features/simulator/SimulatorCursor.java
index 6ff78e19..911872ba 100644
--- a/BauSystem_Main/src/de/steamwar/bausystem/features/simulator/SimulatorCursor.java
+++ b/BauSystem_Main/src/de/steamwar/bausystem/features/simulator/SimulatorCursor.java
@@ -58,10 +58,7 @@ import org.bukkit.event.player.*;
 import org.bukkit.inventory.ItemStack;
 import org.bukkit.util.Vector;
 
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
 import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.stream.Collectors;
@@ -77,6 +74,7 @@ public class SimulatorCursor implements Listener {
 
     private Map<Player, CursorType> cursorType = Collections.synchronizedMap(new HashMap<>());
     private Map<Player, REntityServer> cursors = Collections.synchronizedMap(new HashMap<>());
+    private final Set<Player> calculating = new HashSet<>();
 
     public static boolean isSimulatorItem(ItemStack itemStack) {
         return ItemUtils.isItem(itemStack, "simulator");
@@ -115,6 +113,9 @@ public class SimulatorCursor implements Listener {
     public void onPlayerQuit(PlayerQuitEvent event) {
         cursorType.remove(event.getPlayer());
         cursors.remove(event.getPlayer());
+        synchronized (calculating) {
+            calculating.remove(event.getPlayer());
+        }
     }
 
     private static final Map<Player, Long> LAST_SNEAKS = new HashMap<>();
@@ -141,11 +142,18 @@ public class SimulatorCursor implements Listener {
         }
     }
 
-    public synchronized void calcCursor(Player player) {
+    public void calcCursor(Player player) {
+        synchronized (calculating) {
+            if (calculating.contains(player)) return;
+            calculating.add(player);
+        }
         if (!isSimulatorItem(player.getInventory().getItemInMainHand()) && !isSimulatorItem(player.getInventory().getItemInOffHand())) {
             if (removeCursor(player) || SimulatorWatcher.show(null, player)) {
                 SWUtils.sendToActionbar(player, "");
             }
+            synchronized (calculating) {
+                calculating.remove(player);
+            }
             return;
         }
         Simulator simulator = SimulatorStorage.getSimulator(player);
@@ -160,10 +168,16 @@ public class SimulatorCursor implements Listener {
             } else {
                 SWUtils.sendToActionbar(player, "§eOpen Simulator");
             }
+            synchronized (calculating) {
+                calculating.remove(player);
+            }
             return;
         }
 
         showCursor(player, rayTraceResult, simulator != null);
+        synchronized (calculating) {
+            calculating.remove(player);
+        }
     }
 
     private synchronized boolean removeCursor(Player player) {