diff --git a/src/ytdl_sub/script/types/function.py b/src/ytdl_sub/script/types/function.py
index 566693c1..59aaf8e3 100644
--- a/src/ytdl_sub/script/types/function.py
+++ b/src/ytdl_sub/script/types/function.py
@@ -108,6 +108,9 @@ class BuiltInFunction(Function, BuiltInFunctionType):
         return type(arg)
 
     def output_type(self) -> Type[Resolvable]:
+        if self.function_spec.return_type is ReturnableArgument:
+            generic_arg_index = self.function_spec.args.index(ReturnableArgument)
+            return self._arg_output_type(self.args[generic_arg_index])
         if is_union(self.function_spec.return_type):
             union_types_list = []
             for union_type in self.function_spec.return_type.__args__:
diff --git a/tests/unit/script/functions/test_error_functions.py b/tests/unit/script/functions/test_error_functions.py
index 71943a3d..9f1092b4 100644
--- a/tests/unit/script/functions/test_error_functions.py
+++ b/tests/unit/script/functions/test_error_functions.py
@@ -1,6 +1,7 @@
 import re
 
 import pytest
+from unit.script.conftest import single_variable_output
 
 from ytdl_sub.script.script import Script
 from ytdl_sub.script.utils.exceptions import UserThrownRuntimeError
@@ -16,11 +17,9 @@ class TestErrorFunctions:
             Script({"throw_error": "{%assert(False, 'test this error message')}"}).resolve()
 
     def test_user_assert_passthrough(self):
-        output = (
-            Script({"output": "{%assert(['a'], 'test this error message')}"})
-            .resolve(update=True)
-            .get("output")
-            .native
-        )
-
+        output = single_variable_output("{%assert(['a'], 'test this error message')}")
         assert output == ["a"]
+
+    def test_user_assert_passthrough_as_arg(self):
+        output = single_variable_output("{%int(%assert('123', 'test this error message'))}")
+        assert output == 123