diff --git a/pythonbpf/helper/__init__.py b/pythonbpf/helper/__init__.py
index 1728eb8..17f3198 100644
--- a/pythonbpf/helper/__init__.py
+++ b/pythonbpf/helper/__init__.py
@@ -1,4 +1,4 @@
 from .helper_utils import HelperHandlerRegistry
 from .bpf_helper_handler import handle_helper_call
 
-__all__ = [HelperHandlerRegistry, handle_helper_call]
+__all__ = ["HelperHandlerRegistry", "handle_helper_call"]
diff --git a/pythonbpf/helper/helper_utils.py b/pythonbpf/helper/helper_utils.py
index ed3791b..8e658f0 100644
--- a/pythonbpf/helper/helper_utils.py
+++ b/pythonbpf/helper/helper_utils.py
@@ -1,5 +1,7 @@
 import ast
 import logging
+from collections.abc import Callable
+
 from llvmlite import ir
 from pythonbpf.expr_pass import eval_expr
 
@@ -9,7 +11,7 @@ logger = logging.getLogger(__name__)
 class HelperHandlerRegistry:
     """Registry for BPF helpers"""
 
-    _handlers = {}
+    _handlers: dict[str, Callable] = {}
 
     @classmethod
     def register(cls, helper_name):