diff --git a/src/world/format/Chunk.php b/src/world/format/Chunk.php
index cf11ad540..e842fef96 100644
--- a/src/world/format/Chunk.php
+++ b/src/world/format/Chunk.php
@@ -152,7 +152,7 @@ class Chunk{
 	 * Sets the blockstate at the given coordinate by internal ID.
 	 */
 	public function setFullBlock(int $x, int $y, int $z, int $block) : void{
-		$this->getSubChunk($y >> 4)->setFullBlock($x, $y & 0xf, $z, $block);
+		$this->getWritableSubChunk($y >> 4)->setFullBlock($x, $y & 0xf, $z, $block);
 		$this->dirtyFlags |= self::DIRTY_FLAG_TERRAIN;
 	}
 
@@ -178,12 +178,12 @@ class Chunk{
 	 * @param int $level 0-15
 	 */
 	public function setBlockSkyLight(int $x, int $y, int $z, int $level) : void{
-		$this->getSubChunk($y >> 4)->getBlockSkyLightArray()->set($x & 0xf, $y & 0x0f, $z & 0xf, $level);
+		$this->getWritableSubChunk($y >> 4)->getBlockSkyLightArray()->set($x & 0xf, $y & 0x0f, $z & 0xf, $level);
 	}
 
 	public function setAllBlockSkyLight(int $level) : void{
 		for($y = $this->subChunks->count() - 1; $y >= 0; --$y){
-			$this->getSubChunk($y)->setBlockSkyLightArray(LightArray::fill($level));
+			$this->getWritableSubChunk($y)->setBlockSkyLightArray(LightArray::fill($level));
 		}
 	}
 
@@ -209,12 +209,12 @@ class Chunk{
 	 * @param int $level 0-15
 	 */
 	public function setBlockLight(int $x, int $y, int $z, int $level) : void{
-		$this->getSubChunk($y >> 4)->getBlockLightArray()->set($x & 0xf, $y & 0x0f, $z & 0xf, $level);
+		$this->getWritableSubChunk($y >> 4)->getBlockLightArray()->set($x & 0xf, $y & 0x0f, $z & 0xf, $level);
 	}
 
 	public function setAllBlockLight(int $level) : void{
 		for($y = $this->subChunks->count() - 1; $y >= 0; --$y){
-			$this->getSubChunk($y)->setBlockLightArray(LightArray::fill($level));
+			$this->getWritableSubChunk($y)->setBlockLightArray(LightArray::fill($level));
 		}
 	}
 
@@ -340,10 +340,10 @@ class Chunk{
 		$highestHeightMap = max($this->heightMap->getValues());
 		$lowestFullyLitSubChunk = ($highestHeightMap >> 4) + (($highestHeightMap & 0xf) !== 0 ? 1 : 0);
 		for($y = 0; $y < $lowestFullyLitSubChunk; $y++){
-			$this->getSubChunk($y)->setBlockSkyLightArray(LightArray::fill(0));
+			$this->getWritableSubChunk($y)->setBlockSkyLightArray(LightArray::fill(0));
 		}
 		for($y = $lowestFullyLitSubChunk, $yMax = $this->subChunks->count(); $y < $yMax; $y++){
-			$this->getSubChunk($y)->setBlockSkyLightArray(LightArray::fill(15));
+			$this->getWritableSubChunk($y)->setBlockSkyLightArray(LightArray::fill(15));
 		}
 
 		for($x = 0; $x < 16; ++$x){
@@ -623,6 +623,13 @@ class Chunk{
 		return $this->subChunks[$y];
 	}
 
+	public function getWritableSubChunk(int $y) : SubChunk{
+		if($y < 0 || $y >= $this->subChunks->getSize()){
+			throw new \InvalidArgumentException("Cannot get subchunk $y for writing");
+		}
+		return $this->subChunks[$y];
+	}
+
 	/**
 	 * Sets a subchunk in the chunk index
 	 */
diff --git a/src/world/format/EmptySubChunk.php b/src/world/format/EmptySubChunk.php
index d4beb1931..b28450b0a 100644
--- a/src/world/format/EmptySubChunk.php
+++ b/src/world/format/EmptySubChunk.php
@@ -47,10 +47,6 @@ class EmptySubChunk implements SubChunkInterface{
 		return 0;
 	}
 
-	public function setFullBlock(int $x, int $y, int $z, int $block) : void{
-
-	}
-
 	public function getBlockLayers() : array{
 		return [];
 	}
@@ -63,15 +59,7 @@ class EmptySubChunk implements SubChunkInterface{
 		return new LightArray(LightArray::ZERO);
 	}
 
-	public function setBlockLightArray(LightArray $data) : void{
-
-	}
-
 	public function getBlockSkyLightArray() : LightArray{
 		return new LightArray(LightArray::FIFTEEN);
 	}
-
-	public function setBlockSkyLightArray(LightArray $data) : void{
-
-	}
 }
diff --git a/src/world/format/SubChunkInterface.php b/src/world/format/SubChunkInterface.php
index d2daa72fe..25f4cce28 100644
--- a/src/world/format/SubChunkInterface.php
+++ b/src/world/format/SubChunkInterface.php
@@ -40,8 +40,6 @@ interface SubChunkInterface{
 
 	public function getFullBlock(int $x, int $y, int $z) : int;
 
-	public function setFullBlock(int $x, int $y, int $z, int $block) : void;
-
 	/**
 	 * @return PalettedBlockArray[]
 	 */
@@ -51,9 +49,5 @@ interface SubChunkInterface{
 
 	public function getBlockSkyLightArray() : LightArray;
 
-	public function setBlockSkyLightArray(LightArray $data) : void;
-
 	public function getBlockLightArray() : LightArray;
-
-	public function setBlockLightArray(LightArray $data) : void;
 }
diff --git a/src/world/generator/Flat.php b/src/world/generator/Flat.php
index 5715ffb66..87b8b3fe2 100644
--- a/src/world/generator/Flat.php
+++ b/src/world/generator/Flat.php
@@ -156,7 +156,7 @@ class Flat extends Generator{
 
 		$count = count($this->structure);
 		for($sy = 0; $sy < $count; $sy += 16){
-			$subchunk = $this->chunk->getSubChunk($sy >> 4);
+			$subchunk = $this->chunk->getWritableSubChunk($sy >> 4);
 			for($y = 0; $y < 16 and isset($this->structure[$y | $sy]); ++$y){
 				$id = $this->structure[$y | $sy];
 
diff --git a/src/world/light/LightPopulationTask.php b/src/world/light/LightPopulationTask.php
index 8fa5776e9..b4b33ff86 100644
--- a/src/world/light/LightPopulationTask.php
+++ b/src/world/light/LightPopulationTask.php
@@ -94,10 +94,10 @@ class LightPopulationTask extends AsyncTask{
 			$blockLightArrays = igbinary_unserialize($this->resultBlockLightArrays);
 
 			foreach($skyLightArrays as $y => $array){
-				$chunk->getSubChunk($y)->setBlockSkyLightArray($array);
+				$chunk->getWritableSubChunk($y)->setBlockSkyLightArray($array);
 			}
 			foreach($blockLightArrays as $y => $array){
-				$chunk->getSubChunk($y)->setBlockLightArray($array);
+				$chunk->getWritableSubChunk($y)->setBlockLightArray($array);
 			}
 			$chunk->setLightPopulated();
 		}
diff --git a/tests/phpstan/configs/l8-baseline.neon b/tests/phpstan/configs/l8-baseline.neon
index 506fef3bf..d6678176e 100644
--- a/tests/phpstan/configs/l8-baseline.neon
+++ b/tests/phpstan/configs/l8-baseline.neon
@@ -760,6 +760,11 @@ parameters:
 			count: 1
 			path: ../../../src/world/format/Chunk.php
 
+		-
+			message: "#^Method pocketmine\\\\world\\\\format\\\\Chunk\\:\\:getWritableSubChunk\\(\\) should return pocketmine\\\\world\\\\format\\\\SubChunk but returns pocketmine\\\\world\\\\format\\\\SubChunk\\|null\\.$#"
+			count: 1
+			path: ../../../src/world/format/Chunk.php
+
 		-
 			message: "#^Method pocketmine\\\\world\\\\format\\\\HeightArray\\:\\:get\\(\\) should return int but returns int\\|null\\.$#"
 			count: 1