--- a/net/minecraft/server/WorldBorder.java
+++ b/net/minecraft/server/WorldBorder.java
@@ -15,6 +15,7 @@
     private double g;
     private int h = 29999984;
     private WorldBorder.a i = new WorldBorder.c(6.0E7D);
+    public WorldServer world; // CraftBukkit
 
     public WorldBorder() {}
 
@@ -108,7 +109,7 @@
     }
 
     public void transitionSizeBetween(double d0, double d1, long i) {
-        this.i = (WorldBorder.a) (d0 != d1 ? new WorldBorder.b(d0, d1, i, null) : new WorldBorder.c(d1));
+        this.i = (WorldBorder.a) (d0 != d1 ? new WorldBorder.b(d0, d1, i) : new WorldBorder.c(d1)); // CraftBukkit - decompile error
         Iterator iterator = this.k().iterator();
 
         while (iterator.hasNext()) {
@@ -124,6 +125,7 @@
     }
 
     public void a(IWorldBorderListener iworldborderlistener) {
+        if (a.contains(iworldborderlistener)) return; // CraftBukkit
         this.a.add(iworldborderlistener);
     }