diff --git a/src/pocketmine/level/format/generic/EmptySubChunk.php b/src/pocketmine/level/format/generic/EmptySubChunk.php
index 68efce318..e810b8771 100644
--- a/src/pocketmine/level/format/generic/EmptySubChunk.php
+++ b/src/pocketmine/level/format/generic/EmptySubChunk.php
@@ -108,10 +108,10 @@ class EmptySubChunk extends SubChunk{
 	}
 
 	public function networkSerialize() : string{
-		return str_repeat("\x00", 10240);
+		return "\x00" . str_repeat("\x00", 10240);
 	}
 
 	public function fastSerialize() : string{
-		return "";
+		throw new \BadMethodCallException("Should not try to serialize empty subchunks");
 	}
 }
\ No newline at end of file
diff --git a/src/pocketmine/level/format/generic/GenericChunk.php b/src/pocketmine/level/format/generic/GenericChunk.php
index 6f7c94d8c..5ad0583f7 100644
--- a/src/pocketmine/level/format/generic/GenericChunk.php
+++ b/src/pocketmine/level/format/generic/GenericChunk.php
@@ -628,7 +628,7 @@ class GenericChunk implements Chunk{
 		$count = 0;
 		$subChunks = "";
 		foreach($chunk->subChunks as $y => $subChunk){
-			if($subChunk->isEmpty()){
+			if($subChunk instanceof EmptySubChunk){
 				continue;
 			}
 			++$count;