diff --git a/src/check_jsonschema/cachedownloader.py b/src/check_jsonschema/cachedownloader.py
index 9dd4c0491..932ad303a 100644
--- a/src/check_jsonschema/cachedownloader.py
+++ b/src/check_jsonschema/cachedownloader.py
@@ -100,7 +100,7 @@ class FailedDownloadError(Exception):
 
 
 class CacheDownloader:
-    def __init__(self, cache_dir: str | None = None, disable_cache: bool = False):
+    def __init__(self, cache_dir: str | None = None, disable_cache: bool = False) -> None:
         if cache_dir is None:
             self._cache_dir = _resolve_cache_dir()
         else:
@@ -170,7 +170,7 @@ def __init__(
         downloader: CacheDownloader,
         *,
         validation_callback: t.Callable[[bytes], t.Any] | None = None,
-    ):
+    ) -> None:
         self._file_url = file_url
         self._filename = filename or file_url.split("/")[-1]
         self._downloader = downloader
diff --git a/src/check_jsonschema/checker.py b/src/check_jsonschema/checker.py
index e3e1b9f1e..63d42d4e6 100644
--- a/src/check_jsonschema/checker.py
+++ b/src/check_jsonschema/checker.py
@@ -17,7 +17,7 @@
 
 
 class _Exit(Exception):
-    def __init__(self, code: int):
+    def __init__(self, code: int) -> None:
         self.code = code
 
 
@@ -31,7 +31,7 @@ def __init__(
         format_opts: FormatOptions | None = None,
         traceback_mode: str = "short",
         fill_defaults: bool = False,
-    ):
+    ) -> None:
         self._schema_loader = schema_loader
         self._instance_loader = instance_loader
         self._reporter = reporter
diff --git a/src/check_jsonschema/cli/param_types.py b/src/check_jsonschema/cli/param_types.py
index 234344c95..41ae6846c 100644
--- a/src/check_jsonschema/cli/param_types.py
+++ b/src/check_jsonschema/cli/param_types.py
@@ -117,7 +117,7 @@ def __init__(
         encoding: str | None = None,
         errors: str | None = "strict",
         atomic: bool = False,
-    ):
+    ) -> None:
         self.name: str = os.fspath(filename)
         self.mode = mode
         self.encoding = encoding
diff --git a/src/check_jsonschema/transforms/base.py b/src/check_jsonschema/transforms/base.py
index 327bf0881..0ed9a8647 100644
--- a/src/check_jsonschema/transforms/base.py
+++ b/src/check_jsonschema/transforms/base.py
@@ -10,7 +10,7 @@ def __init__(
         self,
         *,
         on_data: t.Callable[[list | dict], list | dict] | None = None,
-    ):
+    ) -> None:
         self.on_data = on_data
 
     def modify_yaml_implementation(self, implementation: ruamel.yaml.YAML) -> None: