diff --git a/src/main/java/com/sk89q/worldedit/function/mask/BlockMask.java b/src/main/java/com/sk89q/worldedit/function/mask/BlockMask.java
index 1ea91cd46..4228b0deb 100644
--- a/src/main/java/com/sk89q/worldedit/function/mask/BlockMask.java
+++ b/src/main/java/com/sk89q/worldedit/function/mask/BlockMask.java
@@ -50,7 +50,7 @@ public class BlockMask extends AbstractExtentMask {
     public BlockMask(Extent extent, Collection<BaseBlock> blocks) {
         super(extent);
         checkNotNull(blocks);
-        blocks.addAll(blocks);
+        this.blocks.addAll(blocks);
     }
 
     /**
@@ -70,7 +70,7 @@ public class BlockMask extends AbstractExtentMask {
      */
     public void add(Collection<BaseBlock> blocks) {
         checkNotNull(blocks);
-        blocks.addAll(blocks);
+        this.blocks.addAll(blocks);
     }
 
     /**
diff --git a/src/main/java/com/sk89q/worldedit/function/mask/MaskIntersection.java b/src/main/java/com/sk89q/worldedit/function/mask/MaskIntersection.java
index 6c5be470d..3185b42c8 100644
--- a/src/main/java/com/sk89q/worldedit/function/mask/MaskIntersection.java
+++ b/src/main/java/com/sk89q/worldedit/function/mask/MaskIntersection.java
@@ -44,7 +44,7 @@ public class MaskIntersection extends AbstractMask {
      */
     public MaskIntersection(Collection<Mask> masks) {
         checkNotNull(masks);
-        masks.addAll(masks);
+        this.masks.addAll(masks);
     }
 
     /**
@@ -63,7 +63,7 @@ public class MaskIntersection extends AbstractMask {
      */
     public void add(Collection<Mask> masks) {
         checkNotNull(masks);
-        masks.addAll(masks);
+        this.masks.addAll(masks);
     }
 
     /**