diff --git a/src/emerge.h b/src/emerge.h
index 6f204666df707..da845e243e917 100644
--- a/src/emerge.h
+++ b/src/emerge.h
@@ -52,7 +52,6 @@ struct BlockMakeData {
 	u64 seed = 0;
 	v3s16 blockpos_min;
 	v3s16 blockpos_max;
-	v3s16 blockpos_requested;
 	UniqueQueue<v3s16> transforming_liquid;
 	const NodeDefManager *nodedef = nullptr;
 
diff --git a/src/map.cpp b/src/map.cpp
index ef7eddb39ebd5..37b6e9b6b89aa 100644
--- a/src/map.cpp
+++ b/src/map.cpp
@@ -1345,6 +1345,9 @@ bool ServerMap::initBlockMake(v3s16 blockpos, BlockMakeData *data)
 	v3s16 bpmin = EmergeManager::getContainingChunk(blockpos, csize);
 	v3s16 bpmax = bpmin + v3s16(1, 1, 1) * (csize - 1);
 
+	if (!m_chunks_in_progress.insert(bpmin).second)
+		return false;
+
 	bool enable_mapgen_debug_info = m_emerge->enable_mapgen_debug_info;
 	EMERGE_DBG_OUT("initBlockMake(): " PP(bpmin) " - " PP(bpmax));
 
@@ -1360,7 +1363,6 @@ bool ServerMap::initBlockMake(v3s16 blockpos, BlockMakeData *data)
 	data->seed = getSeed();
 	data->blockpos_min = bpmin;
 	data->blockpos_max = bpmax;
-	data->blockpos_requested = blockpos;
 	data->nodedef = m_nodedef;
 
 	/*
@@ -1482,6 +1484,7 @@ void ServerMap::finishBlockMake(BlockMakeData *data,
 		NOTE: Will be saved later.
 	*/
 	//save(MOD_STATE_WRITE_AT_UNLOAD);
+	m_chunks_in_progress.erase(bpmin);
 }
 
 MapSector *ServerMap::createSector(v2s16 p2d)
diff --git a/src/map.h b/src/map.h
index b28f34db30c75..3bc30c482a463 100644
--- a/src/map.h
+++ b/src/map.h
@@ -423,6 +423,7 @@ class ServerMap : public Map
 	// Chunks
 	core::map<v2s16, MapChunk*> m_chunks;
 #endif
+	std::set<v3s16> m_chunks_in_progress;
 
 	/*
 		Metadata is re-written on disk only if this is true.
diff --git a/src/mapgen/mapgen_carpathian.cpp b/src/mapgen/mapgen_carpathian.cpp
index 74ed263ba11ff..b3a0bd270778e 100644
--- a/src/mapgen/mapgen_carpathian.cpp
+++ b/src/mapgen/mapgen_carpathian.cpp
@@ -260,12 +260,6 @@ void MapgenCarpathian::makeChunk(BlockMakeData *data)
 	// Pre-conditions
 	assert(data->vmanip);
 	assert(data->nodedef);
-	assert(data->blockpos_requested.X >= data->blockpos_min.X &&
-			data->blockpos_requested.Y >= data->blockpos_min.Y &&
-			data->blockpos_requested.Z >= data->blockpos_min.Z);
-	assert(data->blockpos_requested.X <= data->blockpos_max.X &&
-			data->blockpos_requested.Y <= data->blockpos_max.Y &&
-			data->blockpos_requested.Z <= data->blockpos_max.Z);
 
 	this->generating = true;
 	this->vm = data->vmanip;
diff --git a/src/mapgen/mapgen_flat.cpp b/src/mapgen/mapgen_flat.cpp
index d62548014db89..3424550291898 100644
--- a/src/mapgen/mapgen_flat.cpp
+++ b/src/mapgen/mapgen_flat.cpp
@@ -209,12 +209,6 @@ void MapgenFlat::makeChunk(BlockMakeData *data)
 	// Pre-conditions
 	assert(data->vmanip);
 	assert(data->nodedef);
-	assert(data->blockpos_requested.X >= data->blockpos_min.X &&
-		data->blockpos_requested.Y >= data->blockpos_min.Y &&
-		data->blockpos_requested.Z >= data->blockpos_min.Z);
-	assert(data->blockpos_requested.X <= data->blockpos_max.X &&
-		data->blockpos_requested.Y <= data->blockpos_max.Y &&
-		data->blockpos_requested.Z <= data->blockpos_max.Z);
 
 	this->generating = true;
 	this->vm   = data->vmanip;
diff --git a/src/mapgen/mapgen_fractal.cpp b/src/mapgen/mapgen_fractal.cpp
index 3b6bbd6c1633b..fabb1b2b197d7 100644
--- a/src/mapgen/mapgen_fractal.cpp
+++ b/src/mapgen/mapgen_fractal.cpp
@@ -209,12 +209,6 @@ void MapgenFractal::makeChunk(BlockMakeData *data)
 	// Pre-conditions
 	assert(data->vmanip);
 	assert(data->nodedef);
-	assert(data->blockpos_requested.X >= data->blockpos_min.X &&
-		data->blockpos_requested.Y >= data->blockpos_min.Y &&
-		data->blockpos_requested.Z >= data->blockpos_min.Z);
-	assert(data->blockpos_requested.X <= data->blockpos_max.X &&
-		data->blockpos_requested.Y <= data->blockpos_max.Y &&
-		data->blockpos_requested.Z <= data->blockpos_max.Z);
 
 	//TimeTaker t("makeChunk");
 
diff --git a/src/mapgen/mapgen_singlenode.cpp b/src/mapgen/mapgen_singlenode.cpp
index cade9e7a8b713..5382423fa1e78 100644
--- a/src/mapgen/mapgen_singlenode.cpp
+++ b/src/mapgen/mapgen_singlenode.cpp
@@ -50,12 +50,6 @@ void MapgenSinglenode::makeChunk(BlockMakeData *data)
 	// Pre-conditions
 	assert(data->vmanip);
 	assert(data->nodedef);
-	assert(data->blockpos_requested.X >= data->blockpos_min.X &&
-		data->blockpos_requested.Y >= data->blockpos_min.Y &&
-		data->blockpos_requested.Z >= data->blockpos_min.Z);
-	assert(data->blockpos_requested.X <= data->blockpos_max.X &&
-		data->blockpos_requested.Y <= data->blockpos_max.Y &&
-		data->blockpos_requested.Z <= data->blockpos_max.Z);
 
 	this->generating = true;
 	this->vm   = data->vmanip;
diff --git a/src/mapgen/mapgen_v5.cpp b/src/mapgen/mapgen_v5.cpp
index 0f6a19fa1be50..87e54755fe32e 100644
--- a/src/mapgen/mapgen_v5.cpp
+++ b/src/mapgen/mapgen_v5.cpp
@@ -201,12 +201,6 @@ void MapgenV5::makeChunk(BlockMakeData *data)
 	// Pre-conditions
 	assert(data->vmanip);
 	assert(data->nodedef);
-	assert(data->blockpos_requested.X >= data->blockpos_min.X &&
-		data->blockpos_requested.Y >= data->blockpos_min.Y &&
-		data->blockpos_requested.Z >= data->blockpos_min.Z);
-	assert(data->blockpos_requested.X <= data->blockpos_max.X &&
-		data->blockpos_requested.Y <= data->blockpos_max.Y &&
-		data->blockpos_requested.Z <= data->blockpos_max.Z);
 
 	this->generating = true;
 	this->vm   = data->vmanip;
diff --git a/src/mapgen/mapgen_v6.cpp b/src/mapgen/mapgen_v6.cpp
index 90a52e0316f63..e04180f96f395 100644
--- a/src/mapgen/mapgen_v6.cpp
+++ b/src/mapgen/mapgen_v6.cpp
@@ -512,12 +512,6 @@ void MapgenV6::makeChunk(BlockMakeData *data)
 	// Pre-conditions
 	assert(data->vmanip);
 	assert(data->nodedef);
-	assert(data->blockpos_requested.X >= data->blockpos_min.X &&
-		data->blockpos_requested.Y >= data->blockpos_min.Y &&
-		data->blockpos_requested.Z >= data->blockpos_min.Z);
-	assert(data->blockpos_requested.X <= data->blockpos_max.X &&
-		data->blockpos_requested.Y <= data->blockpos_max.Y &&
-		data->blockpos_requested.Z <= data->blockpos_max.Z);
 
 	this->generating = true;
 	this->vm   = data->vmanip;
diff --git a/src/mapgen/mapgen_v7.cpp b/src/mapgen/mapgen_v7.cpp
index a1fe25ab6d387..6a7fc567d3828 100644
--- a/src/mapgen/mapgen_v7.cpp
+++ b/src/mapgen/mapgen_v7.cpp
@@ -317,12 +317,6 @@ void MapgenV7::makeChunk(BlockMakeData *data)
 	// Pre-conditions
 	assert(data->vmanip);
 	assert(data->nodedef);
-	assert(data->blockpos_requested.X >= data->blockpos_min.X &&
-		data->blockpos_requested.Y >= data->blockpos_min.Y &&
-		data->blockpos_requested.Z >= data->blockpos_min.Z);
-	assert(data->blockpos_requested.X <= data->blockpos_max.X &&
-		data->blockpos_requested.Y <= data->blockpos_max.Y &&
-		data->blockpos_requested.Z <= data->blockpos_max.Z);
 
 	//TimeTaker t("makeChunk");
 
diff --git a/src/mapgen/mapgen_valleys.cpp b/src/mapgen/mapgen_valleys.cpp
index d7b6f738fafde..c4234857e8afc 100644
--- a/src/mapgen/mapgen_valleys.cpp
+++ b/src/mapgen/mapgen_valleys.cpp
@@ -210,12 +210,6 @@ void MapgenValleys::makeChunk(BlockMakeData *data)
 	// Pre-conditions
 	assert(data->vmanip);
 	assert(data->nodedef);
-	assert(data->blockpos_requested.X >= data->blockpos_min.X &&
-		data->blockpos_requested.Y >= data->blockpos_min.Y &&
-		data->blockpos_requested.Z >= data->blockpos_min.Z);
-	assert(data->blockpos_requested.X <= data->blockpos_max.X &&
-		data->blockpos_requested.Y <= data->blockpos_max.Y &&
-		data->blockpos_requested.Z <= data->blockpos_max.Z);
 
 	//TimeTaker t("makeChunk");