diff --git a/docs/changelog.rst b/docs/changelog.rst
index 80a74785..51cdd2df 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -222,6 +222,10 @@ Core Library
   to a function call, where the reply might be dropped due to exceeding the
   maximum configured message size.
 
+* :gh:issue:`624`: the number of threads used for a child's auto-started thread
+  pool has been reduced from 16 to 2. This may drop to 1 in future, and become
+  configurable via a :class:`Router` option.
+
 * :gh:commit:`a5536c35`: avoid quadratic
   buffer management when logging lines received from a child's redirected
   standard IO.
diff --git a/mitogen/service.py b/mitogen/service.py
index c8022c04..6bd64eb0 100644
--- a/mitogen/service.py
+++ b/mitogen/service.py
@@ -55,7 +55,6 @@ except NameError:
 
 LOG = logging.getLogger(__name__)
 
-DEFAULT_POOL_SIZE = 16
 _pool = None
 _pool_pid = None
 #: Serialize pool construction.
@@ -88,7 +87,7 @@ def get_or_create_pool(size=None, router=None):
                 _pool = Pool(
                     router,
                     services=[],
-                    size=size or DEFAULT_POOL_SIZE,
+                    size=size or 2,
                     overwrite=True,
                     recv=mitogen.core.Dispatcher._service_recv,
                 )