diff --git a/src/mapgen_v5.cpp b/src/mapgen_v5.cpp
index 54fc13745..abea2f714 100644
--- a/src/mapgen_v5.cpp
+++ b/src/mapgen_v5.cpp
@@ -327,7 +327,7 @@ void MapgenV5::calculateNoise()
 		noise_cave2->perlinMap3D(x, y, z);
 	}
 
-	if (node_max.Y >= water_level) {
+	if (node_max.Y >= BIOMEGEN_BASE_V5) {
 		noise_filler_depth->perlinMap2D(x, z);
 		noise_heat->perlinMap2D(x, z);
 		noise_humidity->perlinMap2D(x, z);
@@ -396,7 +396,7 @@ int MapgenV5::generateBaseTerrain()
 
 MgStoneType MapgenV5::generateBiomes(float *heat_map, float *humidity_map)
 {
-	if (node_max.Y < water_level)
+	if (node_max.Y < BIOMEGEN_BASE_V5)
 		return STONE;
 
 	v3s16 em = vm->m_area.getExtent();
@@ -406,74 +406,80 @@ MgStoneType MapgenV5::generateBiomes(float *heat_map, float *humidity_map)
 	for (s16 z = node_min.Z; z <= node_max.Z; z++)
 	for (s16 x = node_min.X; x <= node_max.X; x++, index++) {
 		Biome *biome = NULL;
-		s16 dfiller = 0;
-		s16 y0_top = 0;
-		s16 y0_filler = 0;
-		s16 depth_water_top = 0;
+		u16 depth_top = 0;
+		u16 base_filler = 0;
+		u16 depth_water_top = 0;
+		u32 vi = vm->m_area.index(x, node_max.Y, z);
 
-		s16 nplaced = 0;
-		u32 i = vm->m_area.index(x, node_max.Y, z);
+		// Check node at base of mapchunk above, either a node of a previously
+		// generated mapchunk or if not, a node of overgenerated base terrain.
+		content_t c_above = vm->m_data[vi + em.X].getContent();
+		bool air_above = c_above == CONTENT_AIR;
 
-		content_t c_above = vm->m_data[i + em.X].getContent();
-		bool have_air = c_above == CONTENT_AIR;
+		// If there is air above enable top/filler placement, otherwise force nplaced to
+		// stone level by setting a number that will exceed any possible filler depth.
+		u16 nplaced = (air_above) ? 0 : (u16)-1;
 
 		for (s16 y = node_max.Y; y >= node_min.Y; y--) {
-			content_t c = vm->m_data[i].getContent();
+			content_t c = vm->m_data[vi].getContent();
 
-			if (c != CONTENT_IGNORE && c != CONTENT_AIR &&
-					(y == node_max.Y || have_air)) {
+			// Biome is only (re)calculated for each stone/water upper surface found
+			// below air while working downwards. The chosen biome then remains in
+			// effect for all nodes below until the next biome recalculation.
+			// Biome is (re)calculated when a stone/water node is either: detected
+			// below an air node, or, is at column top and might be underground
+			// or underwater and therefore might not be below air.
+			if (c != CONTENT_AIR && (y == node_max.Y || air_above)) {
 				biome = bmgr->getBiome(heat_map[index], humidity_map[index], y);
-				dfiller = biome->depth_filler + noise_filler_depth->result[index];
-				y0_top = biome->depth_top;
-				y0_filler = biome->depth_top + dfiller;
+				depth_top = biome->depth_top;
+				base_filler = MYMAX(depth_top + biome->depth_filler
+						+ noise_filler_depth->result[index], 0);
 				depth_water_top = biome->depth_water_top;
 
+				// Detect stone type for dungeons during every biome calculation.
+				// This is more efficient than detecting per-node and will not
+				// miss any desert stone or sandstone biomes.
 				if (biome->c_stone == c_desert_stone)
 					stone_type = DESERT_STONE;
 				else if (biome->c_stone == c_sandstone)
 					stone_type = SANDSTONE;
 			}
 
-			if (c == c_stone && have_air) {
-				content_t c_below = vm->m_data[i - em.X].getContent();
+			if (c == c_stone) {
+				content_t c_below = vm->m_data[vi - em.X].getContent();
 
-				if (c_below != CONTENT_AIR && c_below != c_water_source) {
-					if (nplaced < y0_top) {
-						vm->m_data[i] = MapNode(biome->c_top);
-						nplaced++;
-					} else if (nplaced < y0_filler && nplaced >= y0_top) {
-						vm->m_data[i] = MapNode(biome->c_filler);
-						nplaced++;
-					} else if (c == c_stone) {
-						have_air = false;
-						nplaced  = 0;
-						vm->m_data[i] = MapNode(biome->c_stone);
-					} else {
-						have_air = false;
-						nplaced  = 0;
-					}
-				} else if (c == c_stone) {
-					have_air = false;
-					nplaced = 0;
-					vm->m_data[i] = MapNode(biome->c_stone);
+				// If the node below isn't solid, make this node stone, so that
+				// any top/filler nodes above are structurally supported.
+				// This is done by aborting the cycle of top/filler placement
+				// immediately by forcing nplaced to stone level.
+				if (c_below == CONTENT_AIR || c_below == c_water_source)
+					nplaced = (u16)-1;
+
+				if (nplaced < depth_top) {
+					vm->m_data[vi] = MapNode(biome->c_top);
+					nplaced++;
+				} else if (nplaced < base_filler) {
+					vm->m_data[vi] = MapNode(biome->c_filler);
+					nplaced++;
+				} else {
+					vm->m_data[vi] = MapNode(biome->c_stone);
 				}
-			} else if (c == c_stone) {
-				have_air = false;
-				nplaced = 0;
-				vm->m_data[i] = MapNode(biome->c_stone);
+
+				air_above = false;
 			} else if (c == c_water_source) {
-				have_air = true;
-				nplaced = 0;
-				if (y > water_level - depth_water_top)
-					vm->m_data[i] = MapNode(biome->c_water_top);
-				else
-					vm->m_data[i] = MapNode(biome->c_water);
+				vm->m_data[vi] = MapNode((y > (s32)(water_level - depth_water_top)) ?
+						biome->c_water_top : biome->c_water);
+				nplaced = 0;  // Enable top/filler placement for next surface
+				air_above = false;  // Biome is not recalculated underwater
 			} else if (c == CONTENT_AIR) {
-				have_air = true;
-				nplaced = 0;
+				nplaced = 0;  // Enable top/filler placement for next surface
+				air_above = true;  // Biome will be recalculated at next surface
+			} else {  // Possible various nodes overgenerated from neighbouring mapchunks
+				nplaced = (u16)-1;  // Disable top/filler placement
+				air_above = false;
 			}
 
-			vm->m_area.add_y(em, i, -1);
+			vm->m_area.add_y(em, vi, -1);
 		}
 	}
 
diff --git a/src/mapgen_v5.h b/src/mapgen_v5.h
index 5575dfe61..e8455a46f 100644
--- a/src/mapgen_v5.h
+++ b/src/mapgen_v5.h
@@ -23,6 +23,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "mapgen.h"
 
 #define LARGE_CAVE_DEPTH -256
+#define BIOMEGEN_BASE_V5 -192
 
 /////////////////// Mapgen V5 flags
 //#define MGV5_   0x01
diff --git a/src/mapgen_v7.cpp b/src/mapgen_v7.cpp
index 1733fff49..4833699f8 100644
--- a/src/mapgen_v7.cpp
+++ b/src/mapgen_v7.cpp
@@ -362,7 +362,7 @@ void MapgenV7::calculateNoise()
 		noise_mount_height->perlinMap2D(x, z);
 	}
 
-	if (node_max.Y >= water_level) {
+	if (node_max.Y >= BIOMEGEN_BASE_V7) {
 		noise_filler_depth->perlinMap2D(x, z);
 		noise_heat->perlinMap2D(x, z);
 		noise_humidity->perlinMap2D(x, z);
@@ -591,7 +591,7 @@ void MapgenV7::generateRidgeTerrain()
 
 MgStoneType MapgenV7::generateBiomes(float *heat_map, float *humidity_map)
 {
-	if (node_max.Y < water_level)
+	if (node_max.Y < BIOMEGEN_BASE_V7)
 		return STONE;
 
 	v3s16 em = vm->m_area.getExtent();
@@ -601,74 +601,80 @@ MgStoneType MapgenV7::generateBiomes(float *heat_map, float *humidity_map)
 	for (s16 z = node_min.Z; z <= node_max.Z; z++)
 	for (s16 x = node_min.X; x <= node_max.X; x++, index++) {
 		Biome *biome = NULL;
-		s16 dfiller = 0;
-		s16 y0_top = 0;
-		s16 y0_filler = 0;
-		s16 depth_water_top = 0;
+		u16 depth_top = 0;
+		u16 base_filler = 0;
+		u16 depth_water_top = 0;
+		u32 vi = vm->m_area.index(x, node_max.Y, z);
 
-		s16 nplaced = 0;
-		u32 i = vm->m_area.index(x, node_max.Y, z);
+		// Check node at base of mapchunk above, either a node of a previously
+		// generated mapchunk or if not, a node of overgenerated base terrain.
+		content_t c_above = vm->m_data[vi + em.X].getContent();
+		bool air_above = c_above == CONTENT_AIR;
 
-		content_t c_above = vm->m_data[i + em.X].getContent();
-		bool have_air = c_above == CONTENT_AIR;
+		// If there is air above enable top/filler placement, otherwise force nplaced to
+		// stone level by setting a number that will exceed any possible filler depth.
+		u16 nplaced = (air_above) ? 0 : (u16)-1;
 
 		for (s16 y = node_max.Y; y >= node_min.Y; y--) {
-			content_t c = vm->m_data[i].getContent();
+			content_t c = vm->m_data[vi].getContent();
 
-			if (c != CONTENT_IGNORE && c != CONTENT_AIR &&
-					(y == node_max.Y || have_air)) {
+			// Biome is only (re)calculated for each stone/water upper surface found
+			// below air while working downwards. The chosen biome then remains in
+			// effect for all nodes below until the next biome recalculation.
+			// Biome is (re)calculated when a stone/water node is either: detected
+			// below an air node, or, is at column top and might be underground
+			// or underwater and therefore might not be below air.
+			if (c != CONTENT_AIR && (y == node_max.Y || air_above)) {
 				biome = bmgr->getBiome(heat_map[index], humidity_map[index], y);
-				dfiller = biome->depth_filler + noise_filler_depth->result[index];
-				y0_top = biome->depth_top;
-				y0_filler = biome->depth_top + dfiller;
+				depth_top = biome->depth_top;
+				base_filler = MYMAX(depth_top + biome->depth_filler
+						+ noise_filler_depth->result[index], 0);
 				depth_water_top = biome->depth_water_top;
 
+				// Detect stone type for dungeons during every biome calculation.
+				// This is more efficient than detecting per-node and will not
+				// miss any desert stone or sandstone biomes.
 				if (biome->c_stone == c_desert_stone)
 					stone_type = DESERT_STONE;
 				else if (biome->c_stone == c_sandstone)
 					stone_type = SANDSTONE;
 			}
 
-			if (c == c_stone && have_air) {
-				content_t c_below = vm->m_data[i - em.X].getContent();
+			if (c == c_stone) {
+				content_t c_below = vm->m_data[vi - em.X].getContent();
 
-				if (c_below != CONTENT_AIR && c_below != c_water_source) {
-					if (nplaced < y0_top) {
-						vm->m_data[i] = MapNode(biome->c_top);
-						nplaced++;
-					} else if (nplaced < y0_filler && nplaced >= y0_top) {
-						vm->m_data[i] = MapNode(biome->c_filler);
-						nplaced++;
-					} else if (c == c_stone) {
-						have_air = false;
-						nplaced  = 0;
-						vm->m_data[i] = MapNode(biome->c_stone);
-					} else {
-						have_air = false;
-						nplaced  = 0;
-					}
-				} else if (c == c_stone) {
-					have_air = false;
-					nplaced = 0;
-					vm->m_data[i] = MapNode(biome->c_stone);
+				// If the node below isn't solid, make this node stone, so that
+				// any top/filler nodes above are structurally supported.
+				// This is done by aborting the cycle of top/filler placement
+				// immediately by forcing nplaced to stone level.
+				if (c_below == CONTENT_AIR || c_below == c_water_source)
+					nplaced = (u16)-1;
+
+				if (nplaced < depth_top) {
+					vm->m_data[vi] = MapNode(biome->c_top);
+					nplaced++;
+				} else if (nplaced < base_filler) {
+					vm->m_data[vi] = MapNode(biome->c_filler);
+					nplaced++;
+				} else {
+					vm->m_data[vi] = MapNode(biome->c_stone);
 				}
-			} else if (c == c_stone) {
-				have_air = false;
-				nplaced = 0;
-				vm->m_data[i] = MapNode(biome->c_stone);
+
+				air_above = false;
 			} else if (c == c_water_source) {
-				have_air = true;
-				nplaced = 0;
-				if (y > water_level - depth_water_top)
-					vm->m_data[i] = MapNode(biome->c_water_top);
-				else
-					vm->m_data[i] = MapNode(biome->c_water);
+				vm->m_data[vi] = MapNode((y > (s32)(water_level - depth_water_top)) ?
+						biome->c_water_top : biome->c_water);
+				nplaced = 0;  // Enable top/filler placement for next surface
+				air_above = false;  // Biome is not recalculated underwater
 			} else if (c == CONTENT_AIR) {
-				have_air = true;
-				nplaced = 0;
+				nplaced = 0;  // Enable top/filler placement for next surface
+				air_above = true;  // Biome will be recalculated at next surface
+			} else {  // Possible various nodes overgenerated from neighbouring mapchunks
+				nplaced = (u16)-1;  // Disable top/filler placement
+				air_above = false;
 			}
 
-			vm->m_area.add_y(em, i, -1);
+			vm->m_area.add_y(em, vi, -1);
 		}
 	}
 
diff --git a/src/mapgen_v7.h b/src/mapgen_v7.h
index eb46c371b..84f0c9efa 100644
--- a/src/mapgen_v7.h
+++ b/src/mapgen_v7.h
@@ -22,6 +22,8 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 #include "mapgen.h"
 
+#define BIOMEGEN_BASE_V7 -192
+
 /////////////////// Mapgen V7 flags
 #define MGV7_MOUNTAINS   0x01
 #define MGV7_RIDGES      0x02