diff --git a/src/duty/validation.py b/src/duty/validation.py
index 4858916..6976cf0 100644
--- a/src/duty/validation.py
+++ b/src/duty/validation.py
@@ -8,6 +8,7 @@
 from __future__ import annotations
 
 import sys
+import textwrap
 from functools import cached_property
 from inspect import Parameter, Signature, signature
 from typing import Any, Callable, Sequence
@@ -48,16 +49,14 @@ def cast_arg(arg: Any, annotation: Any) -> Any:
 class ParamsCaster:
     """A helper class to cast parameters based on a function's signature annotations."""
 
-    def __init__(self, function: Callable) -> None:
+    def __init__(self, signature: Signature) -> None:
         """Initialize the object.
 
         Parameters:
-            function: The function to use to cast arguments.
+            signature: The signature to use to cast arguments.
         """
-        self.function = function
-        self.signature = signature(function)
-        self.params_dict = self.signature.parameters
-        self.params_list = list(self.params_dict.values())[1:]
+        self.params_dict = signature.parameters
+        self.params_list = list(self.params_dict.values())
 
     @cached_property
     def var_positional_position(self) -> int:
@@ -168,6 +167,52 @@ def cast(self, *args: Any, **kwargs: Any) -> tuple[Sequence, dict[str, Any]]:
         return positional, keyword
 
 
+def _get_params_caster(func: Callable, *args: Any, **kwargs: Any) -> ParamsCaster:
+    duties_module = sys.modules[func.__module__]
+    exec_globals = dict(duties_module.__dict__)
+    eval_str = False
+    for name in list(exec_globals.keys()):
+        if exec_globals[name] is annotations:
+            eval_str = True
+            del exec_globals[name]
+    exec_globals["__context_above"] = {}
+
+    # Don't keep first parameter: context.
+    params = list(signature(func).parameters.values())[1:]
+    params_no_types = [Parameter(param.name, param.kind, default=param.default) for param in params]
+    code_sig = Signature(parameters=params_no_types)
+    if eval_str:
+        params_types = [
+            Parameter(
+                param.name,
+                param.kind,
+                default=param.default,
+                annotation=eval(  # noqa: PGH001
+                    param.annotation,
+                    exec_globals,
+                ),
+            )
+            for param in params
+        ]
+    else:
+        params_types = params
+    cast_sig = Signature(parameters=params_types)
+
+    code = f"""
+        import inspect
+        def {func.__name__}{code_sig}: ...
+        __context_above['func'] = {func.__name__}
+    """
+
+    exec(textwrap.dedent(code), exec_globals)  # noqa: S102
+    func = exec_globals["__context_above"]["func"]
+
+    # Trigger TypeError early.
+    func(*args, **kwargs)
+
+    return ParamsCaster(cast_sig)
+
+
 def validate(
     func: Callable,
     *args: Any,
@@ -190,14 +235,4 @@ def validate(
     Returns:
         The casted arguments.
     """
-    name = func.__name__
-
-    # don't keep first parameter: context
-    params_list = list(signature(func).parameters.values())[1:]
-    params = [Parameter(param.name, param.kind, default=param.default) for param in params_list]
-    sig = Signature(parameters=params)
-    trixx: dict = {}
-    exec(f"def {name}{sig}: ...\ntrixx[0] = {name}")  # noqa: S102
-    trixx[0](*args, **kwargs)
-    caster = ParamsCaster(func)
-    return caster.cast(*args, **kwargs)
+    return _get_params_caster(func, *args, **kwargs).cast(*args, **kwargs)
diff --git a/tests/test_validation.py b/tests/test_validation.py
index e7fb3e2..fddc4ca 100644
--- a/tests/test_validation.py
+++ b/tests/test_validation.py
@@ -7,7 +7,7 @@
 
 import pytest
 
-from duty.validation import ParamsCaster, cast_arg, to_bool
+from duty.validation import _get_params_caster, cast_arg, to_bool
 from tests.fixtures import validation as valfix
 
 
@@ -130,7 +130,7 @@ def test_params_caster(func: Callable, args: tuple, kwargs: dict, expected_args:
         expected_args: The expected positional arguments result.
         expected_kwargs: The expected keyword arguments result.
     """
-    caster = ParamsCaster(func)
+    caster = _get_params_caster(func, *args, **kwargs)
     new_args, new_kwargs = caster.cast(*args, **kwargs)
     assert new_args == expected_args
     assert new_kwargs == expected_kwargs