diff --git a/picamera2/picamera2.py b/picamera2/picamera2.py
index 5827f75d..903372bc 100644
--- a/picamera2/picamera2.py
+++ b/picamera2/picamera2.py
@@ -237,6 +237,7 @@ def __init__(self, camera_num=0, verbose_console=None, tuning=None):
         self.notifymeread = os.fdopen(self.notifyme_r, 'rb')
         self._cm.add(camera_num, self)
         self.camera_idx = camera_num
+        self.request_lock = threading.Lock()  # global lock used by requests
         self._requestslock = threading.Lock()
         self._requests = []
         if verbose_console is None:
diff --git a/picamera2/request.py b/picamera2/request.py
index a54e12af..12c7e213 100644
--- a/picamera2/request.py
+++ b/picamera2/request.py
@@ -1,6 +1,5 @@
 import io
 import logging
-import threading
 import time
 from datetime import datetime
 from pathlib import Path
@@ -102,15 +101,17 @@ class CompletedRequest:
     def __init__(self, request, picam2):
         self.request = request
         self.ref_count = 1
-        self.lock = threading.Lock()
+        self.lock = picam2.request_lock
         self.picam2 = picam2
         self.stop_count = picam2.stop_count
         self.configure_count = picam2.configure_count
         self.config = self.picam2.camera_config.copy()
         self.stream_map = self.picam2.stream_map.copy()
-        self.syncs = [picam2.allocator.sync(self.picam2.allocator, buffer, False) for buffer in self.request.buffers.values()]
-        self.picam2.allocator.acquire(self.request.buffers)
-        [sync.__enter__() for sync in self.syncs]
+        with self.lock:
+            self.syncs = [picam2.allocator.sync(self.picam2.allocator, buffer, False)
+                          for buffer in self.request.buffers.values()]
+            self.picam2.allocator.acquire(self.request.buffers)
+            [sync.__enter__() for sync in self.syncs]
 
     def acquire(self):
         """Acquire a reference to this completed request, which stops it being recycled back to the camera system."""