diff --git a/core/src/mindustry/game/EventType.java b/core/src/mindustry/game/EventType.java
index 015eac0c97..9d590de52c 100644
--- a/core/src/mindustry/game/EventType.java
+++ b/core/src/mindustry/game/EventType.java
@@ -9,6 +9,7 @@ import mindustry.net.*;
 import mindustry.net.Packets.*;
 import mindustry.type.*;
 import mindustry.world.*;
+import mindustry.world.blocks.storage.CoreBlock.*;
 
 public class EventType{
 
@@ -283,6 +284,15 @@ public class EventType{
         }
     }
 
+    /** Called when a core block is placed/removed or its team is changed. */
+    public static class CoreChangeEvent{
+        public CoreBuild core;
+
+        public CoreChangeEvent(CoreBuild core){
+            this.core = core;
+        }
+    }
+
     public static class StateChangeEvent{
         public final State from, to;
 
diff --git a/core/src/mindustry/graphics/OverlayRenderer.java b/core/src/mindustry/graphics/OverlayRenderer.java
index fe7309621e..a75555b60b 100644
--- a/core/src/mindustry/graphics/OverlayRenderer.java
+++ b/core/src/mindustry/graphics/OverlayRenderer.java
@@ -28,22 +28,24 @@ public class OverlayRenderer{
     private float buildFade, unitFade;
     private Sized lastSelect;
     private Seq<CoreEdge> cedges = new Seq<>();
-    private int lastCores = -1;
+    private boolean updatedCores;
 
     public OverlayRenderer(){
         Events.on(WorldLoadEvent.class, e -> {
-            cedges.clear();
-            lastCores = -1;
+            updatedCores = true;
+        });
+
+        Events.on(CoreChangeEvent.class, e -> {
+            updatedCores = true;
         });
     }
 
     private void updateCoreEdges(){
-        int count = state.teams.active.sum(t -> t.cores.size);
-        if(count == lastCores){
+        if(!updatedCores){
             return;
         }
 
-        lastCores = count;
+        updatedCores = false;
         cedges.clear();
 
         Seq<Vec2> pos = new Seq<>();
@@ -55,6 +57,7 @@ public class OverlayRenderer{
             }
         }
 
+        //if this is laggy, it could be shoved in another thread.
         var result = Voronoi.generate(pos.toArray(Vec2.class), 0, world.unitWidth(), 0, world.unitHeight());
         for(var edge : result){
             cedges.add(new CoreEdge(edge.x1, edge.y1, edge.x2, edge.y2, teams.get(edge.site1).team, teams.get(edge.site2).team));
diff --git a/core/src/mindustry/world/blocks/storage/CoreBlock.java b/core/src/mindustry/world/blocks/storage/CoreBlock.java
index a5d61237e3..52844719d7 100644
--- a/core/src/mindustry/world/blocks/storage/CoreBlock.java
+++ b/core/src/mindustry/world/blocks/storage/CoreBlock.java
@@ -194,6 +194,20 @@ public class CoreBlock extends StorageBlock{
             super.damage(source, damage);
         }
 
+        @Override
+        public void created(){
+            super.created();
+
+            Events.fire(new CoreChangeEvent(this));
+        }
+
+        @Override
+        public void changeTeam(Team next){
+            super.changeTeam(next);
+
+            Events.fire(new CoreChangeEvent(this));
+        }
+
         @Override
         public double sense(LAccess sensor){
             if(sensor == LAccess.itemCapacity) return storageCapacity;
@@ -260,6 +274,8 @@ public class CoreBlock extends StorageBlock{
                     spawner.getSpawns().add(tile);
                 }
             }
+
+            Events.fire(new CoreChangeEvent(this));
         }
 
         @Override