diff --git a/src/appier/http.py b/src/appier/http.py
index 6495affe..8c0bfb2f 100644
--- a/src/appier/http.py
+++ b/src/appier/http.py
@@ -908,10 +908,20 @@ def _client_netius(level=logging.CRITICAL):
     if netius_client:
         return netius_client
 
+    # reaps stale clients from dead threads before creating
+    # a new one, this prevents unbounded growth of the global
+    # clients map in long-running multi-threaded applications
+    _reap_netius_clients()
+
     # creates the "new" HTTP client for the current thread and registers
-    # it under the netius client structure so that it may be re-used
+    # it under the netius client structure so that it may be re-used, the
+    # insertion is done inside the lock to avoid TOCTOU race conditions
     netius_client = netius.clients.HTTPClient(auto_release=False)
-    _netius_clients[tid] = netius_client
+    ACCESS_LOCK.acquire()
+    try:
+        _netius_clients[tid] = netius_client
+    finally:
+        ACCESS_LOCK.release()
 
     # in case this is the first registration of the dictionary a new on
     # exit callback is registered to cleanup the netius infra-structure
@@ -983,6 +993,26 @@ def _callback(protocol, parser, message):
     return extra
 
 
+def _reap_netius_clients():
+    global _netius_clients
+    if not _netius_clients:
+        return
+    live_tids = set(t.ident for t in threading.enumerate())
+    ACCESS_LOCK.acquire()
+    try:
+        dead_tids = [tid for tid in _netius_clients if tid not in live_tids]
+        for tid in dead_tids:
+            client = _netius_clients.pop(tid, None)
+            if not client:
+                continue
+            try:
+                client.cleanup()
+            except Exception:
+                pass
+    finally:
+        ACCESS_LOCK.release()
+
+
 def _cleanup_netius():
     global _netius_clients
     for netius_client in _netius_clients.values():
diff --git a/src/appier/test/http.py b/src/appier/test/http.py
index 56926122..605fd0ac 100644
--- a/src/appier/test/http.py
+++ b/src/appier/test/http.py
@@ -29,6 +29,7 @@
 """ The license for the module """
 
 import unittest
+import unittest.mock
 import threading
 
 import appier
@@ -262,3 +263,50 @@ def test_invalid(self):
         self.assertRaises(
             BaseException, lambda: appier.get("https://invalidlargedomain.org/")
         )
+
+    def test_reap_netius_clients(self):
+        dead_client = unittest.mock.MagicMock()
+        alive_client = unittest.mock.MagicMock()
+
+        alive_tid = threading.current_thread().ident
+        dead_tid = 99999999
+
+        original = getattr(appier.http, "_netius_clients", None)
+        try:
+            appier.http._netius_clients = {
+                dead_tid: dead_client,
+                alive_tid: alive_client,
+            }
+
+            appier.http._reap_netius_clients()
+
+            self.assertEqual(dead_tid in appier.http._netius_clients, False)
+            self.assertEqual(alive_tid in appier.http._netius_clients, True)
+            dead_client.cleanup.assert_called_once()
+            alive_client.cleanup.assert_not_called()
+        finally:
+            if original is None:
+                if hasattr(appier.http, "_netius_clients"):
+                    del appier.http._netius_clients
+            else:
+                appier.http._netius_clients = original
+
+    def test_client_netius_cleanup(self):
+        dead_client = unittest.mock.MagicMock()
+        dead_tid = 99999999
+
+        original = getattr(appier.http, "_netius_clients", None)
+        try:
+            appier.http._netius_clients = {dead_tid: dead_client}
+
+            appier.http._reap_netius_clients()
+
+            self.assertEqual(dead_tid in appier.http._netius_clients, False)
+            self.assertEqual(len(appier.http._netius_clients), 0)
+            dead_client.cleanup.assert_called_once()
+        finally:
+            if original is None:
+                if hasattr(appier.http, "_netius_clients"):
+                    del appier.http._netius_clients
+            else:
+                appier.http._netius_clients = original