diff --git a/core/src/main/java/com/boydti/fawe/jnbt/anvil/HeightMapMCAGenerator.java b/core/src/main/java/com/boydti/fawe/jnbt/anvil/HeightMapMCAGenerator.java
index c495dc47..70cf8c1b 100644
--- a/core/src/main/java/com/boydti/fawe/jnbt/anvil/HeightMapMCAGenerator.java
+++ b/core/src/main/java/com/boydti/fawe/jnbt/anvil/HeightMapMCAGenerator.java
@@ -1058,6 +1058,13 @@ public class HeightMapMCAGenerator extends MCAWriter implements SimpleWorld, Faw
         return heights.getByte(index) & 0xFF;
     }
 
+    @Override
+    public int getNearestSurfaceTerrainBlock(int x, int z, int y, int minY, int maxY, int failedMin, int failedMax) {
+        int index = z * getWidth() + x;
+        if (index < 0 || index >= getArea()) index = Math.floorMod(index, getArea());
+        return heights.getByte(index) & 0xFF;
+    }
+
     public void setBiome(BufferedImage img, byte biome, boolean white) {
         if (img.getWidth() != getWidth() || img.getHeight() != getLength())
             throw new IllegalArgumentException("Input image dimensions do not match the current height map!");
diff --git a/core/src/main/java/com/boydti/fawe/object/queue/IDelegateFaweQueue.java b/core/src/main/java/com/boydti/fawe/object/queue/IDelegateFaweQueue.java
index d8d5acf6..a000c271 100644
--- a/core/src/main/java/com/boydti/fawe/object/queue/IDelegateFaweQueue.java
+++ b/core/src/main/java/com/boydti/fawe/object/queue/IDelegateFaweQueue.java
@@ -483,6 +483,11 @@ public interface IDelegateFaweQueue extends FaweQueue {
         return getQueue().getNearestSurfaceTerrainBlock(x, z, y, minY, maxY);
     }
 
+    @Override
+    default int getNearestSurfaceTerrainBlock(int x, int z, int y, int minY, int maxY, int failedMin, int failedMax) {
+        return getQueue().getNearestSurfaceTerrainBlock(x, z, y, minY, maxY, failedMin, failedMax);
+    }
+
     @Override
     default void addCaves(Region region) throws WorldEditException {
         getQueue().addCaves(region);
diff --git a/core/src/main/java/com/sk89q/worldedit/extent/AbstractDelegateExtent.java b/core/src/main/java/com/sk89q/worldedit/extent/AbstractDelegateExtent.java
index 86dc8344..456d80a3 100644
--- a/core/src/main/java/com/sk89q/worldedit/extent/AbstractDelegateExtent.java
+++ b/core/src/main/java/com/sk89q/worldedit/extent/AbstractDelegateExtent.java
@@ -202,6 +202,11 @@ public class AbstractDelegateExtent implements LightingExtent {
         return extent.getNearestSurfaceTerrainBlock(x, z, y, minY, maxY);
     }
 
+    @Override
+    public int getNearestSurfaceTerrainBlock(int x, int z, int y, int minY, int maxY, int failedMin, int failedMax) {
+        return extent.getNearestSurfaceTerrainBlock(x, z, y, minY, maxY, failedMin, failedMax);
+    }
+
     @Override
     public final
     @Nullable
diff --git a/core/src/main/java/com/sk89q/worldedit/extent/Extent.java b/core/src/main/java/com/sk89q/worldedit/extent/Extent.java
index 15eb366b..7a709c56 100644
--- a/core/src/main/java/com/sk89q/worldedit/extent/Extent.java
+++ b/core/src/main/java/com/sk89q/worldedit/extent/Extent.java
@@ -118,10 +118,14 @@ public interface Extent extends InputExtent, OutputExtent {
                 }
             }
         }
-        return maxY << 4;
+        return (state ? minY : maxY) << 4;
     }
 
     public default int getNearestSurfaceTerrainBlock(int x, int z, int y, int minY, int maxY) {
+        return getNearestSurfaceTerrainBlock(x, z, y, minY, maxY, minY, maxY);
+    }
+
+    public default int getNearestSurfaceTerrainBlock(int x, int z, int y, int minY, int maxY, int failedMin, int failedMax) {
         y = Math.max(minY, Math.min(maxY, y));
         int clearanceAbove = maxY - y;
         int clearanceBelow = y - minY;
@@ -150,7 +154,7 @@ public interface Extent extends InputExtent, OutputExtent {
                 }
             }
         }
-        return maxY == 255 && minY == 0 ? maxY : -1;
+        return state ? failedMin : failedMax;
     }
 
     default public void addCaves(Region region) throws WorldEditException {
diff --git a/core/src/main/java/com/sk89q/worldedit/math/convolution/HeightMap.java b/core/src/main/java/com/sk89q/worldedit/math/convolution/HeightMap.java
index cc8d1c5b..b6c8e3e2 100644
--- a/core/src/main/java/com/sk89q/worldedit/math/convolution/HeightMap.java
+++ b/core/src/main/java/com/sk89q/worldedit/math/convolution/HeightMap.java
@@ -25,6 +25,7 @@ public class HeightMap {
 
     private final boolean layers;
     private int[] data;
+    private boolean[] invalid;
     private int width;
     private int height;
 
@@ -62,12 +63,12 @@ public class HeightMap {
         int minZ = region.getMinimumPoint().getBlockZ();
         int maxY = region.getMaximumPoint().getBlockY();
 
+        data = new int[width * height];
+        invalid = new boolean[data.length];
+
         if (layers) {
             Vector min = region.getMinimumPoint();
             Vector max = region.getMaximumPoint();
-            int width = region.getWidth();
-            int height = region.getLength();
-            data = new int[width * height];
             int bx = min.getBlockX();
             int bz = min.getBlockZ();
             Iterable<Vector2D> flat = Regions.asFlatRegion(region).asFlatRegion();
@@ -83,7 +84,6 @@ public class HeightMap {
             }
         } else {
             // Store current heightmap data
-            data = new int[width * height];
             int index = 0;
             if (naturalOnly) {
                 for (int z = 0; z < height; ++z) {
@@ -95,13 +95,25 @@ public class HeightMap {
                 int yTmp = 255;
                 for (int z = 0; z < height; ++z) {
                     for (int x = 0; x < width; ++x, index++) {
-                        data[index] = yTmp = session.getNearestSurfaceTerrainBlock(x + minX, z + minZ, yTmp, minY, maxY);
+                        yTmp = session.getNearestSurfaceTerrainBlock(x + minX, z + minZ, yTmp, minY, maxY, Integer.MIN_VALUE, Integer.MAX_VALUE);
+                        switch (yTmp) {
+                            case Integer.MIN_VALUE:
+                                yTmp = minY;
+                                invalid[index] = true;
+                                break;
+                            case Integer.MAX_VALUE:
+                                yTmp = maxY;
+                                invalid[index] = true;
+                                break;
+                        }
+                        data[index] = yTmp;
                     }
                 }
             }
         }
     }
 
+    @Deprecated
     public HeightMap(EditSession session, Region region, int[] data, boolean layers) {
         this.session = session;
         this.region = region;
@@ -179,7 +191,7 @@ public class HeightMap {
             int zr = z + originZ;
             for (int x = 0; x < width; ++x) {
                 int curHeight = this.data[index];
-                if (curHeight == -1) continue;
+                if (this.invalid != null && this.invalid[index]) continue;
                 int newHeight = Math.min(maxY4, data[index++]);
                 int curBlock = (curHeight) >> 3;
                 int newBlock = (newHeight + 7) >> 3;
@@ -235,7 +247,6 @@ public class HeightMap {
     }
 
     public int apply(int[] data) throws WorldEditException {
-        long start = System.currentTimeMillis();
         checkNotNull(data);
 
         Vector minY = region.getMinimumPoint();
@@ -254,10 +265,11 @@ public class HeightMap {
         int index = 0;
         for (int z = 0; z < height; ++z) {
             int zr = z + originZ;
-            for (int x = 0; x < width; ++x) {
+            for (int x = 0; x < width; ++x, index++) {
                 int curHeight = this.data[index];
-                if (curHeight == -1) continue;
-                int newHeight = Math.min(maxY, data[index++]);
+                if (this.invalid != null && this.invalid[index]) continue;
+                int newHeight = Math.min(maxY, data[index]);
+
                 int xr = x + originX;
 
                 // Depending on growing or shrinking we need to start at the bottom or top