diff --git a/docs/conf.py b/docs/conf.py
index 2df277f4..bc77b700 100755
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -275,7 +275,7 @@ htmlhelp_basename = 'ocrmypdfdoc'
 
 # -- Options for LaTeX output ---------------------------------------------
 
-latex_elements = {
+latex_elements = {  # type: ignore
     # The paper size ('letterpaper' or 'a4paper').
     #
     # 'papersize': 'letterpaper',
diff --git a/src/ocrmypdf/_validation.py b/src/ocrmypdf/_validation.py
index cb55c454..5c595f5e 100644
--- a/src/ocrmypdf/_validation.py
+++ b/src/ocrmypdf/_validation.py
@@ -13,7 +13,7 @@ import sys
 import unicodedata
 from pathlib import Path
 from shutil import copyfileobj
-from typing import List, Set, Tuple, Union
+from typing import List, Set, Tuple
 
 import pikepdf
 import PIL
@@ -182,10 +182,8 @@ def _pages_from_ranges(ranges: str) -> Set[int]:
 
 def check_options_ocr_behavior(options):
     exclusive_options = sum(
-        
-            (1 if opt else 0)
-            for opt in (options.force_ocr, options.skip_text, options.redo_ocr)
-        
+        (1 if opt else 0)
+        for opt in (options.force_ocr, options.skip_text, options.redo_ocr)
     )
     if exclusive_options >= 2:
         raise BadArgsError("Choose only one of --force-ocr, --skip-text, --redo-ocr.")
diff --git a/src/ocrmypdf/leptonica.py b/src/ocrmypdf/leptonica.py
index 9f2554de..a053b43d 100644
--- a/src/ocrmypdf/leptonica.py
+++ b/src/ocrmypdf/leptonica.py
@@ -66,7 +66,7 @@ if os.name == 'nt':
     # Loading zlib from other places could cause a version mismatch
     _zlib_path = os.path.join(os.path.dirname(_libpath), 'zlib1.dll')
     if not os.path.exists(_zlib_path):
-        _zlib_path = find_library('zlib')
+        _zlib_path = find_library('zlib') or ''
     try:
         zlib = ffi.dlopen(_zlib_path)
     except ffi.error as e:
diff --git a/src/ocrmypdf/optimize.py b/src/ocrmypdf/optimize.py
index fce66464..0df62327 100644
--- a/src/ocrmypdf/optimize.py
+++ b/src/ocrmypdf/optimize.py
@@ -365,6 +365,7 @@ def convert_to_jbig2(
     When the JBIG2 symbolic coder is not used, each JBIG2 stands on its own
     and needs no dictionary. Currently this must be lossless JBIG2.
     """
+    jbig2_globals_dict: Optional[Dictionary]
 
     _produce_jbig2_images(jbig2_groups, root, options, executor)
 
diff --git a/src/ocrmypdf/pluginspec.py b/src/ocrmypdf/pluginspec.py
index 47de64b6..c7db3e93 100644
--- a/src/ocrmypdf/pluginspec.py
+++ b/src/ocrmypdf/pluginspec.py
@@ -197,7 +197,7 @@ def rasterize_pdf_page(
 
 
 @hookspec(firstresult=True)
-def filter_ocr_image(page: 'PageContext', image: 'Image') -> 'Image':
+def filter_ocr_image(page: 'PageContext', image: Image.Image) -> Image.Image:
     """Called to filter the image before it is sent to OCR.
 
     This is the image that OCR sees, not what the user sees when they view the