diff --git a/lib/wongi/engine/dsl.ex b/lib/wongi/engine/dsl.ex
index 08f2eb8..cafef5f 100644
--- a/lib/wongi/engine/dsl.ex
+++ b/lib/wongi/engine/dsl.ex
@@ -137,7 +137,7 @@ defmodule Wongi.Engine.DSL do
   @doc """
   A filter that passes if the value is a unary function that returns true.
 
-  The function will receive the variable as its argument.
+  The function will receive the variable value as its argument.
   """
   def filter(var, func), do: Filter.new(Function.new(var, func))
 
diff --git a/lib/wongi/engine/filter/function.ex b/lib/wongi/engine/filter/function.ex
index 366c71e..b6676cc 100644
--- a/lib/wongi/engine/filter/function.ex
+++ b/lib/wongi/engine/filter/function.ex
@@ -11,6 +11,8 @@ defmodule Wongi.Engine.Filter.Function do
   end
 
   defimpl Wongi.Engine.Filter do
+    alias Wongi.Engine.Filter.Common
+
     def pass?(%@for{var: nil, func: func}, _token) when is_function(func, 0) do
       func.()
     end
@@ -20,7 +22,7 @@ defmodule Wongi.Engine.Filter.Function do
     end
 
     def pass?(%@for{var: var, func: func}, token) when is_function(func, 1) do
-      func.(token[var])
+      func.(Common.resolve(var, token))
     end
   end
 end
diff --git a/mix.exs b/mix.exs
index 4ad091c..4f44f94 100644
--- a/mix.exs
+++ b/mix.exs
@@ -4,7 +4,7 @@ defmodule Wongi.Engine.MixProject do
   def project do
     [
       app: :wongi_engine,
-      version: "0.9.13",
+      version: "0.9.14",
       elixir: "~> 1.15",
       elixirc_paths: elixirc_paths(Mix.env()),
       start_permanent: Mix.env() == :prod,
diff --git a/test/wongi/engine/filter/function_test.exs b/test/wongi/engine/filter/function_test.exs
index dede23b..eb86b3c 100644
--- a/test/wongi/engine/filter/function_test.exs
+++ b/test/wongi/engine/filter/function_test.exs
@@ -40,7 +40,7 @@ defmodule Wongi.Engine.Filter.FunctionTest do
         rule(
           forall: [
             has(:a, :b, var(:x)),
-            filter(:x, &__MODULE__.true?/1)
+            filter(var(:x), &__MODULE__.true?/1)
           ]
         )
       )