diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index ff10f765..eb7716ca 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -30,3 +30,12 @@ repos:
     hooks:
       - id: pyupgrade
         args: ["--py36-plus"]
+  - repo: https://github.com/pre-commit/mirrors-mypy
+    rev: v0.910
+    hooks:
+      - id: mypy
+        additional_dependencies:
+          - types-toml
+          - types-setuptools
+          - types-requests
+          - types-Pillow
diff --git a/src/ocrmypdf/_exec/tesseract.py b/src/ocrmypdf/_exec/tesseract.py
index 25f09bbd..33ead41e 100644
--- a/src/ocrmypdf/_exec/tesseract.py
+++ b/src/ocrmypdf/_exec/tesseract.py
@@ -20,6 +20,7 @@ from typing import List, Optional
 
 from PIL import Image
 
+from ocrmypdf.api import StrPath
 from ocrmypdf.exceptions import (
     MissingDependencyError,
     SubprocessOutputError,
@@ -250,7 +251,8 @@ def generate_hocr(
 
     # Reminder: test suite tesseract test plugins will break after any changes
     # to the number of order parameters here
-    args_tesseract.extend([input_file, prefix, 'hocr', 'txt'] + tessconfig)
+    args_tesseract.extend([os.fspath(input_file), os.fspath(prefix), 'hocr', 'txt'])
+    args_tesseract.extend(tessconfig)
     try:
         p = run(args_tesseract, stdout=PIPE, stderr=STDOUT, timeout=timeout, check=True)
         stdout = p.stdout
@@ -324,7 +326,8 @@ def generate_pdf(
     # Reminder: test suite tesseract test plugins might break after any changes
     # to the number of order parameters here
 
-    args_tesseract.extend([input_file, prefix, 'pdf', 'txt'] + tessconfig)
+    args_tesseract.extend([os.fspath(input_file), os.fspath(prefix), 'pdf', 'txt'])
+    args_tesseract.extend(tessconfig)
     try:
         p = run(args_tesseract, stdout=PIPE, stderr=STDOUT, timeout=timeout, check=True)
         stdout = p.stdout
diff --git a/src/ocrmypdf/api.py b/src/ocrmypdf/api.py
index 65ab910b..de3561e4 100644
--- a/src/ocrmypdf/api.py
+++ b/src/ocrmypdf/api.py
@@ -31,7 +31,7 @@ except ModuleNotFoundError:
     coloredlogs = None
 
 
-StrPath = Union[os.PathLike, AnyStr]
+StrPath = Union[Path, AnyStr]
 PathOrIO = Union[BinaryIO, StrPath]
 
 _api_lock = threading.Lock()
diff --git a/src/ocrmypdf/cli.py b/src/ocrmypdf/cli.py
index 43ea1de7..199e0c41 100644
--- a/src/ocrmypdf/cli.py
+++ b/src/ocrmypdf/cli.py
@@ -6,7 +6,7 @@
 
 
 import argparse
-from typing import Optional, Type, TypeVar
+from typing import Any, Callable, Optional, TypeVar
 
 from ocrmypdf._version import PROGRAM_NAME as _PROGRAM_NAME
 from ocrmypdf._version import __version__ as _VERSION
@@ -14,7 +14,9 @@ from ocrmypdf._version import __version__ as _VERSION
 T = TypeVar('T')
 
 
-def numeric(basetype: Type[T], min_: Optional[T] = None, max_: Optional[T] = None):
+def numeric(
+    basetype: Callable[[Any], T], min_: Optional[T] = None, max_: Optional[T] = None
+):
     """Validator for numeric params"""
     min_ = basetype(min_) if min_ is not None else None
     max_ = basetype(max_) if max_ is not None else None