diff --git a/worldedit-core/src/main/java/com/sk89q/worldedit/EditSession.java b/worldedit-core/src/main/java/com/sk89q/worldedit/EditSession.java
index 159fcf0be..ca4700db6 100644
--- a/worldedit-core/src/main/java/com/sk89q/worldedit/EditSession.java
+++ b/worldedit-core/src/main/java/com/sk89q/worldedit/EditSession.java
@@ -3566,7 +3566,7 @@ public class EditSession extends PassthroughExtent implements AutoCloseable {
                 double scaledZ = (z - zero.getZ()) / unit.getZ();
 
                 try {
-                    if (expression.evaluate(timeout, scaledX, scaledY, scaledZ) <= 0) {
+                    if (expression.evaluate(new double[]{scaledX, scaledY, scaledZ}, timeout) <= 0) {
                         return null;
                     }
 
diff --git a/worldedit-core/src/main/java/com/sk89q/worldedit/command/GenerationCommands.java b/worldedit-core/src/main/java/com/sk89q/worldedit/command/GenerationCommands.java
index 54f78e983..d63f26e52 100644
--- a/worldedit-core/src/main/java/com/sk89q/worldedit/command/GenerationCommands.java
+++ b/worldedit-core/src/main/java/com/sk89q/worldedit/command/GenerationCommands.java
@@ -443,7 +443,8 @@ public class GenerationCommands {
             @Selection Region region,
             @Arg(desc = "The biome type to set")
                     BiomeType target,
-            @Arg(desc = "Expression to test block placement locations and set biome type", variable = true)
+            @Arg(desc = "Expression to test block placement locations and set biome type. Requires x,y,z variables be present",
+                    variable = true)
                     List<String> expression,
             @Switch(name = 'h', desc = "Generate a hollow shape")
                     boolean hollow,