diff --git a/src/ocrmypdf/_exec/jbig2enc.py b/src/ocrmypdf/_exec/jbig2enc.py
index 9311ec3f..2e8a058b 100644
--- a/src/ocrmypdf/_exec/jbig2enc.py
+++ b/src/ocrmypdf/_exec/jbig2enc.py
@@ -41,9 +41,17 @@ def convert_group(*, cwd, infiles, out_prefix):
     return proc
 
 
+def convert_group_mp(args):
+    return convert_group(cwd=args[0], infiles=args[1], out_prefix=args[2])
+
+
 def convert_single(*, cwd, infile, outfile):
     args = ['jbig2', '-p', infile]
     with open(outfile, 'wb') as fstdout:
         proc = run(args, cwd=cwd, stdout=fstdout, stderr=PIPE)
     proc.check_returncode()
     return proc
+
+
+def convert_single_mp(args):
+    return convert_single(cwd=args[0], infile=args[1], outfile=args[2])
diff --git a/src/ocrmypdf/_exec/pngquant.py b/src/ocrmypdf/_exec/pngquant.py
index d7e345f2..12dc79bc 100644
--- a/src/ocrmypdf/_exec/pngquant.py
+++ b/src/ocrmypdf/_exec/pngquant.py
@@ -61,3 +61,7 @@ def quantize(input_file: Path, output_file: Path, quality_min: int, quality_max:
     if result.returncode == 0:
         # input_file could be the same as output_file, so we defer the write
         output_file.write_bytes(result.stdout)
+
+
+def quantize_mp(args):
+    return quantize(*args)
diff --git a/src/ocrmypdf/optimize.py b/src/ocrmypdf/optimize.py
index c097e32e..3724f731 100644
--- a/src/ocrmypdf/optimize.py
+++ b/src/ocrmypdf/optimize.py
@@ -212,7 +212,10 @@ def extract_image_generic(
 
 
 def extract_images(
-    pike: Pdf, root: Path, options, extract_fn: Callable[..., Optional[XrefExt]],
+    pike: Pdf,
+    root: Path,
+    options,
+    extract_fn: Callable[..., Optional[XrefExt]],
 ) -> Iterator[Tuple[int, XrefExt]]:
     """Extract image using extract_fn
 
@@ -305,10 +308,10 @@ def _produce_jbig2_images(
     def jbig2_group_args(root: Path, groups: Dict[int, List[XrefExt]]):
         for group, xref_exts in groups.items():
             prefix = f'group{group:08d}'
-            yield dict(
-                cwd=fspath(root),
-                infiles=(img_name(root, xref, ext) for xref, ext in xref_exts),
-                out_prefix=prefix,
+            yield (
+                fspath(root),  # =cwd
+                (img_name(root, xref, ext) for xref, ext in xref_exts),  # =infiles
+                prefix,  # =out_prefix
             )
 
     def jbig2_single_args(root, groups: Dict[int, List[XrefExt]]):
@@ -317,21 +320,18 @@ def _produce_jbig2_images(
             # Second loop is to ensure multiple images per page are unpacked
             for n, xref_ext in enumerate(xref_exts):
                 xref, ext = xref_ext
-                yield dict(
-                    cwd=fspath(root),
-                    infile=img_name(root, xref, ext),
-                    outfile=root / f'{prefix}.{n:04d}',
+                yield (
+                    fspath(root),
+                    img_name(root, xref, ext),
+                    root / f'{prefix}.{n:04d}',
                 )
 
-    def convert_generic(fn, kwargs_dict):
-        return fn(**kwargs_dict)
-
     if options.jbig2_page_group_size > 1:
         jbig2_args = jbig2_group_args
-        jbig2_convert = partial(convert_generic, jbig2enc.convert_group)
+        jbig2_convert = jbig2enc.convert_group_mp
     else:
         jbig2_args = jbig2_single_args
-        jbig2_convert = partial(convert_generic, jbig2enc.convert_single)
+        jbig2_convert = jbig2enc.convert_single_mp
 
     exec_progress_pool(
         use_threads=True,
@@ -476,9 +476,6 @@ def transcode_pngs(
                 )
                 modified.add(xref)
 
-        def pngquant_fn(args):
-            pngquant.quantize(*args)
-
         exec_progress_pool(
             use_threads=True,
             max_workers=options.jobs,
@@ -488,7 +485,7 @@ def transcode_pngs(
                 unit='image',
                 disable=not options.progress_bar,
             ),
-            task=pngquant_fn,
+            task=pngquant.quantize_mp,
             task_arguments=pngquant_args(),
         )