--- ../src-base/minecraft/net/minecraft/entity/EntityTracker.java
+++ ../src-work/minecraft/net/minecraft/entity/EntityTracker.java
@@ -38,6 +38,7 @@
 import net.minecraft.world.chunk.Chunk;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import net.minecraft.server.MinecraftServer; // Spigot
 
 import cpw.mods.fml.common.registry.EntityRegistry;
 
@@ -45,8 +46,8 @@
 {
     private static final Logger logger = LogManager.getLogger();
     private final WorldServer theWorld;
-    private Set trackedEntities = new HashSet();
-    private IntHashMap trackedEntityIDs = new IntHashMap();
+    private Set<EntityTrackerEntry> trackedEntities = new pw.prok.imagine.collections.IndirectSet<EntityTrackerEntry>();
+    public IntHashMap trackedEntityIDs = new IntHashMap(); // CraftBukkit - private -> public
     private int entityViewDistance;
     private static final String __OBFID = "CL_00001431";
 
@@ -73,7 +74,7 @@
             {
                 EntityTrackerEntry entitytrackerentry = (EntityTrackerEntry)iterator.next();
 
-                if (entitytrackerentry.myEntity != entityplayermp)
+                if (entitytrackerentry != null && entitytrackerentry.myEntity != entityplayermp)
                 {
                     entitytrackerentry.tryStartWachingThis(entityplayermp);
                 }
@@ -184,6 +185,7 @@
 
     public void addEntityToTracker(Entity p_72785_1_, int p_72785_2_, final int p_72785_3_, boolean p_72785_4_)
     {
+        p_72785_2_ = org.spigotmc.TrackingRange.getEntityTrackingRange(p_72785_1_, p_72785_2_); // Spigot
         if (p_72785_2_ > this.entityViewDistance)
         {
             p_72785_2_ = this.entityViewDistance;
@@ -193,7 +195,7 @@
         {
             if (this.trackedEntityIDs.containsItem(p_72785_1_.getEntityId()))
             {
-                throw new IllegalStateException("Entity is already tracked!");
+                return;
             }
 
             EntityTrackerEntry entitytrackerentry = new EntityTrackerEntry(p_72785_1_, p_72785_2_, p_72785_3_, p_72785_4_);
@@ -223,7 +225,9 @@
             });
             p_72785_1_.addEntityCrashInfo(crashreportcategory);
             CrashReportCategory crashreportcategory1 = crashreport.makeCategory("Entity That Is Already Tracked");
+            try {
             ((EntityTrackerEntry)this.trackedEntityIDs.lookup(p_72785_1_.getEntityId())).myEntity.addEntityCrashInfo(crashreportcategory1);
+            } catch(Exception ignored) {}
 
             try
             {
@@ -246,6 +250,7 @@
             while (iterator.hasNext())
             {
                 EntityTrackerEntry entitytrackerentry = (EntityTrackerEntry)iterator.next();
+                if (entitytrackerentry != null)
                 entitytrackerentry.removeFromWatchingList(entityplayermp);
             }
         }
@@ -267,12 +272,14 @@
         while (iterator.hasNext())
         {
             EntityTrackerEntry entitytrackerentry = (EntityTrackerEntry)iterator.next();
+            if (entitytrackerentry != null) {
             entitytrackerentry.sendLocationToAllClients(this.theWorld.playerEntities);
 
             if (entitytrackerentry.playerEntitiesUpdated && entitytrackerentry.myEntity instanceof EntityPlayerMP)
             {
                 arraylist.add((EntityPlayerMP)entitytrackerentry.myEntity);
             }
+            }
         }
 
         for (int i = 0; i < arraylist.size(); ++i)
@@ -284,12 +291,13 @@
             {
                 EntityTrackerEntry entitytrackerentry1 = (EntityTrackerEntry)iterator1.next();
 
-                if (entitytrackerentry1.myEntity != entityplayermp)
+                if (entitytrackerentry1 != null && entitytrackerentry1.myEntity != entityplayermp)
                 {
                     entitytrackerentry1.tryStartWachingThis(entityplayermp);
                 }
             }
         }
+        ((pw.prok.imagine.collections.Indirect) trackedEntities).compat(theWorld.getTotalWorldTime() % 100 == 0);
     }
 
     public void func_151247_a(Entity p_151247_1_, Packet p_151247_2_)
@@ -319,6 +327,7 @@
         while (iterator.hasNext())
         {
             EntityTrackerEntry entitytrackerentry = (EntityTrackerEntry)iterator.next();
+            if (entitytrackerentry != null)
             entitytrackerentry.removePlayerFromTracker(p_72787_1_);
         }
     }
@@ -331,7 +340,7 @@
         {
             EntityTrackerEntry entitytrackerentry = (EntityTrackerEntry)iterator.next();
 
-            if (entitytrackerentry.myEntity != p_85172_1_ && entitytrackerentry.myEntity.chunkCoordX == p_85172_2_.xPosition && entitytrackerentry.myEntity.chunkCoordZ == p_85172_2_.zPosition)
+            if (entitytrackerentry != null && entitytrackerentry.myEntity != p_85172_1_ && entitytrackerentry.myEntity.chunkCoordX == p_85172_2_.xPosition && entitytrackerentry.myEntity.chunkCoordZ == p_85172_2_.zPosition)
             {
                 entitytrackerentry.tryStartWachingThis(p_85172_1_);
             }