diff --git a/core/src/mindustry/io/TypeIO.java b/core/src/mindustry/io/TypeIO.java
index c0ee5f6d9f29..21ad470fd74b 100644
--- a/core/src/mindustry/io/TypeIO.java
+++ b/core/src/mindustry/io/TypeIO.java
@@ -128,6 +128,9 @@ public static void writeObject(Writes write, Object object){
             for(Object obj : objs){
                 writeObject(write, obj);
             }
+        }else if(object instanceof UnitCommand command){
+            write.b(23);
+            write.s(command.id);
         }else{
             throw new IllegalArgumentException("Unknown object type: " + object.getClass());
         }
@@ -200,6 +203,7 @@ public static Object readObjectBoxed(Reads read, boolean box){
                 for(int i = 0; i < objlen; i++) objs[i] = readObjectBoxed(read, box);
                 yield objs;
             }
+            case 23 -> UnitCommand.all.get(read.us());
             default -> throw new IllegalArgumentException("Unknown object type: " + type);
         };
     }
diff --git a/core/src/mindustry/world/Block.java b/core/src/mindustry/world/Block.java
index 126a269cc5ad..088a933753bf 100644
--- a/core/src/mindustry/world/Block.java
+++ b/core/src/mindustry/world/Block.java
@@ -890,6 +890,11 @@ public void placeBegan(Tile tile, Block previous){
 
     }
 
+    /** Called when building of this block begins. */
+    public void placeBegan(Tile tile, Block previous, @Nullable Unit builder){
+        placeBegan(tile, previous);
+    }
+
     /** Called right before building of this block begins. */
     public void beforePlaceBegan(Tile tile, Block previous){
 
diff --git a/core/src/mindustry/world/Build.java b/core/src/mindustry/world/Build.java
index ecec0e1c04a2..e5a9064930f3 100644
--- a/core/src/mindustry/world/Build.java
+++ b/core/src/mindustry/world/Build.java
@@ -115,9 +115,9 @@ public static void beginPlace(@Nullable Unit unit, Block result, Team team, int
         build.prevBuild = prevBuild;
         if(unit != null && unit.getControllerName() != null) build.lastAccessed = unit.getControllerName();
 
-        result.placeBegan(tile, previous);
-
         Events.fire(new BlockBuildBeginEvent(tile, team, unit, false));
+
+        result.placeBegan(tile, previous, unit);
     }
 
     /** Returns whether a tile can be placed at this location by this team. */
diff --git a/core/src/mindustry/world/blocks/storage/CoreBlock.java b/core/src/mindustry/world/blocks/storage/CoreBlock.java
index d33ee51ece16..b09b005bcda4 100644
--- a/core/src/mindustry/world/blocks/storage/CoreBlock.java
+++ b/core/src/mindustry/world/blocks/storage/CoreBlock.java
@@ -164,7 +164,7 @@ public boolean canPlaceOn(Tile tile, Team team, int rotation){
     }
 
     @Override
-    public void placeBegan(Tile tile, Block previous){
+    public void placeBegan(Tile tile, Block previous, Unit builder){
         //finish placement immediately when a block is replaced.
         if(previous instanceof CoreBlock){
             tile.setBlock(this, tile.team());
@@ -181,6 +181,8 @@ public void placeBegan(Tile tile, Block previous){
 
                 nextItems = null;
             }
+
+            Events.fire(new BlockBuildEndEvent(tile, builder, tile.team(), false, null));
         }
     }