diff --git a/worldedit-core/src/main/java/com/sk89q/worldedit/command/RegionCommands.java b/worldedit-core/src/main/java/com/sk89q/worldedit/command/RegionCommands.java
index be2a307b9..4a8c1840d 100644
--- a/worldedit-core/src/main/java/com/sk89q/worldedit/command/RegionCommands.java
+++ b/worldedit-core/src/main/java/com/sk89q/worldedit/command/RegionCommands.java
@@ -36,6 +36,7 @@ import com.sk89q.worldedit.entity.Player;
 import com.sk89q.worldedit.extension.platform.Actor;
 import com.sk89q.worldedit.function.GroundFunction;
 import com.sk89q.worldedit.function.generator.FloraGenerator;
+import com.sk89q.worldedit.function.mask.AbstractExtentMask;
 import com.sk89q.worldedit.function.mask.ExistingBlockMask;
 import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.function.mask.MaskIntersection;
@@ -300,6 +301,9 @@ public class RegionCommands {
         if (from == null) {
             from = new ExistingBlockMask(editSession);
         }
+        if (from instanceof AbstractExtentMask) {
+            ((AbstractExtentMask) from).setExtent(editSession);
+        }
         int affected = editSession.replaceBlocks(region, from, to);
         actor.printInfo(TranslatableComponent.of("worldedit.replace.replaced", TextComponent.of(affected)));
         return affected;
diff --git a/worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BiomeMask.java b/worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BiomeMask.java
index 8189d583e..202efefec 100644
--- a/worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BiomeMask.java
+++ b/worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BiomeMask.java
@@ -34,9 +34,8 @@ import static com.google.common.base.Preconditions.checkNotNull;
 /**
  * Tests true if the biome at applied points is the same as the one given.
  */
-public class BiomeMask extends AbstractMask {
+public class BiomeMask extends AbstractExtentMask {
 
-    private final Extent extent;
     private final Set<BiomeType> biomes = new HashSet<>();
 
     /**
@@ -46,9 +45,8 @@ public class BiomeMask extends AbstractMask {
      * @param biomes a list of biomes to match
      */
     public BiomeMask(Extent extent, Collection<BiomeType> biomes) {
-        checkNotNull(extent);
+        super(extent);
         checkNotNull(biomes);
-        this.extent = extent;
         this.biomes.addAll(biomes);
     }
 
@@ -92,7 +90,7 @@ public class BiomeMask extends AbstractMask {
 
     @Override
     public boolean test(BlockVector3 vector) {
-        BiomeType biome = extent.getBiome(vector);
+        BiomeType biome = getExtent().getBiome(vector);
         return biomes.contains(biome);
     }
 
@@ -104,7 +102,12 @@ public class BiomeMask extends AbstractMask {
 
     @Override
     public Mask copy() {
-        return new BiomeMask(extent, new HashSet<>(biomes));
+        return new BiomeMask(getExtent(), new HashSet<>(biomes));
     }
 
+    @Override
+    public boolean test(Extent extent, BlockVector3 position) {
+        BiomeType biome = getExtent().getBiome(position);
+        return biomes.contains(biome);
+    }
 }