diff --git a/src/mapblock.cpp b/src/mapblock.cpp
index d0fbe1c38..767919c56 100644
--- a/src/mapblock.cpp
+++ b/src/mapblock.cpp
@@ -104,9 +104,9 @@ MapBlock::MapBlock(v3s16 pos, IGameDef *gamedef):
 		m_pos(pos),
 		m_pos_relative(pos * MAP_BLOCKSIZE),
 		m_gamedef(gamedef),
-		m_is_mono_block(true)
+		m_is_mono_block(false)
 {
-	reallocate(1, MapNode(CONTENT_IGNORE));
+	reallocate(nodecount, MapNode(CONTENT_IGNORE));
 }
 
 MapBlock::~MapBlock()
diff --git a/src/unittest/test_mapblock.cpp b/src/unittest/test_mapblock.cpp
index 98e184141..d81848580 100644
--- a/src/unittest/test_mapblock.cpp
+++ b/src/unittest/test_mapblock.cpp
@@ -57,21 +57,25 @@ void TestMapBlock::runTests(IGameDef *gamedef)
 void TestMapBlock::testMonoblock(IGameDef *gamedef)
 {
 	MapBlock block({}, gamedef);
-	UASSERT(block.m_is_mono_block);
-	block.data[0] = MapNode(CONTENT_AIR);
+	UASSERT(!block.m_is_mono_block);
 
 	// make the array is expanded
 	block.expandNodesIfNeeded();
-	UASSERT(std::all_of(block.data, block.data + MapBlock::nodecount, [](MapNode &n) { return n == MapNode(CONTENT_AIR); }));
+	UASSERT(std::all_of(block.data, block.data + MapBlock::nodecount, [](MapNode &n) { return n == MapNode(CONTENT_IGNORE); }));
 
 	// covert to monoblock
 	block.tryShrinkNodes();
 	UASSERT(block.m_is_mono_block);
+	UASSERT(block.data[0].param0 == CONTENT_IGNORE);
+
+	block.data[0] = MapNode(CONTENT_AIR);
+	UASSERT(block.m_is_mono_block);
 	UASSERT(block.data[0].param0 == CONTENT_AIR);
 
 	// get the data(), should deconvert the block
 	block.getData();
 	UASSERT(!block.m_is_mono_block);
+	UASSERT(std::all_of(block.data, block.data + MapBlock::nodecount, [](MapNode &n) { return n == MapNode(CONTENT_AIR); }));
 
 	// covert back to mono block
 	block.tryShrinkNodes();