diff --git a/src/ytdl_sub/script/script.py b/src/ytdl_sub/script/script.py
index f7c20d88..ab506318 100644
--- a/src/ytdl_sub/script/script.py
+++ b/src/ytdl_sub/script/script.py
@@ -490,15 +490,18 @@ class Script:
             name: definition for name, definition in variables.items() if not _is_function(name)
         }
 
+        custom_function_names = set(self._functions.keys()) | functions_to_add.keys()
+        variable_names = (
+            set(self._variables.keys()) | variables_to_add.keys() | (unresolvable or set())
+        )
+
         for definitions in [functions_to_add, variables_to_add]:
             for name, definition in definitions.items():
                 parsed = parse(
                     text=definition,
                     name=name,
-                    custom_function_names=set(self._functions.keys()),
-                    variable_names=set(self._variables.keys())
-                    .union(variables.keys())
-                    .union(unresolvable or set()),
+                    custom_function_names=custom_function_names,
+                    variable_names=variable_names,
                 )
 
                 if parsed.maybe_resolvable is None:
diff --git a/tests/unit/script/types/test_custom_function.py b/tests/unit/script/types/test_custom_function.py
index e7b76e80..61096cc3 100644
--- a/tests/unit/script/types/test_custom_function.py
+++ b/tests/unit/script/types/test_custom_function.py
@@ -22,6 +22,24 @@ class TestCustomFunction:
             }
         ).resolve() == ScriptOutput({"output": Integer(9)})
 
+    def test_custom_functions_any_order_via_add(self):
+        assert Script({}).add(
+            {
+                "%custom_cubed": "{%mul(%custom_square($0),$0)}",
+                "%custom_square": "{%mul($0, $0)}",
+                "output": "{%custom_cubed(3)}",
+            }
+        ).resolve() == ScriptOutput({"output": Integer(27)})
+
+    def test_custom_functions_any_order_via_init(self):
+        assert Script(
+            {
+                "%custom_cubed": "{%mul(%custom_square($0),$0)}",
+                "%custom_square": "{%mul($0, $0)}",
+                "output": "{%custom_cubed(3)}",
+            }
+        ).resolve() == ScriptOutput({"output": Integer(27)})
+
     def test_custom_function_cycle(self):
         with pytest.raises(
             CycleDetected, match=re.escape("The custom function %cycle_func cannot call itself.")