diff --git a/src/ocrmypdf/_concurrent.py b/src/ocrmypdf/_concurrent.py
index 87c9656c..e3fb5b91 100644
--- a/src/ocrmypdf/_concurrent.py
+++ b/src/ocrmypdf/_concurrent.py
@@ -4,8 +4,11 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
+import threading
 from typing import Callable, Iterable, Optional
 
+pool_lock = threading.Lock()
+
 
 def _task_noop(*_args, **_kwargs):
     return
@@ -35,12 +38,13 @@ def exec_progress_pool(
     if not task_finished:
         task_finished = _task_noop
 
-    _model(
-        use_threads=use_threads,
-        max_workers=max_workers,
-        tqdm_kwargs=tqdm_kwargs,
-        worker_initializer=worker_initializer,
-        task=task,
-        task_arguments=task_arguments,
-        task_finished=task_finished,
-    )
+    with pool_lock:
+        _model(
+            use_threads=use_threads,
+            max_workers=max_workers,
+            tqdm_kwargs=tqdm_kwargs,
+            worker_initializer=worker_initializer,
+            task=task,
+            task_arguments=task_arguments,
+            task_finished=task_finished,
+        )
diff --git a/src/ocrmypdf/builtin_plugins/concurrency.py b/src/ocrmypdf/builtin_plugins/concurrency.py
index 7d7fbbfc..3b3e0d74 100644
--- a/src/ocrmypdf/builtin_plugins/concurrency.py
+++ b/src/ocrmypdf/builtin_plugins/concurrency.py
@@ -31,8 +31,6 @@ from ocrmypdf.exceptions import InputFileError
 
 Queue = Union[multiprocessing.Queue, queue.Queue]
 
-pool_lock = threading.Lock()
-
 
 def log_listener(q: Queue):
     """Listen to the worker processes and forward the messages to logging
@@ -120,18 +118,17 @@ def exec_progress_pool(
 
         worker_initializer = _noop
 
-    with pool_lock:
-        _exec_progress_pool(
-            max_workers=max_workers,
-            tqdm_kwargs=tqdm_kwargs,
-            worker_initializer=worker_initializer,
-            task=task,
-            task_arguments=task_arguments,
-            task_finished=task_finished,
-            log_queue=log_queue,
-            pool_class=pool_class,
-            initializer=initializer,
-        )
+    _exec_progress_pool(
+        max_workers=max_workers,
+        tqdm_kwargs=tqdm_kwargs,
+        worker_initializer=worker_initializer,
+        task=task,
+        task_arguments=task_arguments,
+        task_finished=task_finished,
+        log_queue=log_queue,
+        pool_class=pool_class,
+        initializer=initializer,
+    )
 
 
 def _exec_progress_pool(
diff --git a/src/ocrmypdf/extra_plugins/awslambda.py b/src/ocrmypdf/extra_plugins/awslambda.py
index 3a5f802d..4f7a7af7 100644
--- a/src/ocrmypdf/extra_plugins/awslambda.py
+++ b/src/ocrmypdf/extra_plugins/awslambda.py
@@ -11,7 +11,6 @@
 import logging
 import logging.handlers
 import signal
-import threading
 from contextlib import suppress
 from enum import Enum, auto
 from itertools import islice, repeat, takewhile, zip_longest
@@ -23,8 +22,6 @@ from unittest.mock import Mock
 from ocrmypdf import hookimpl
 from ocrmypdf.exceptions import InputFileError
 
-pool_lock = threading.Lock()
-
 
 class MessageType(Enum):
     exception = auto()
@@ -101,15 +98,14 @@ def lambda_pool_impl(
             task_finished(result, pbar)
         return
 
-    with pool_lock:
-        _lambda_pool_impl(
-            max_workers=max_workers,
-            worker_initializer=worker_initializer,
-            task=task,
-            task_arguments=task_arguments,
-            task_finished=task_finished,
-            pbar=pbar,
-        )
+    _lambda_pool_impl(
+        max_workers=max_workers,
+        worker_initializer=worker_initializer,
+        task=task,
+        task_arguments=task_arguments,
+        task_finished=task_finished,
+        pbar=pbar,
+    )
 
 
 def _lambda_pool_impl(