diff --git a/warcprox/main.py b/warcprox/main.py
index 3ad92fe..de7ce89 100644
--- a/warcprox/main.py
+++ b/warcprox/main.py
@@ -74,13 +74,13 @@ def _build_arg_parser(prog=os.path.basename(sys.argv[0])):
     arg_parser.add_argument('--rethinkdb-big-table',
             dest='rethinkdb_big_table', action='store_true', default=False,
             help='use a big rethinkdb table called "captures", instead of a small table called "dedup"; table is suitable for use as index for playback (ignored unless --rethinkdb-servers is specified)')
-    arg_parser.add_argument('--kafka-broker-list', dest='kafka_broker_list', 
+    arg_parser.add_argument('--kafka-broker-list', dest='kafka_broker_list',
             default=None, help='kafka broker list for capture feed')
-    arg_parser.add_argument('--kafka-capture-feed-topic', dest='kafka_capture_feed_topic', 
+    arg_parser.add_argument('--kafka-capture-feed-topic', dest='kafka_capture_feed_topic',
             default=None, help='kafka capture feed topic')
     arg_parser.add_argument('--queue-size', dest='queue_size', default=500,
             help=argparse.SUPPRESS)
-    arg_parser.add_argument('--max-threads', dest='max_threads', default=500,
+    arg_parser.add_argument('--max-threads', dest='max_threads',
             help=argparse.SUPPRESS)
     arg_parser.add_argument('--profile', action='store_true', default=False,
             help=argparse.SUPPRESS)
diff --git a/warcprox/warcproxy.py b/warcprox/warcproxy.py
index b46f610..b9ed3ec 100644
--- a/warcprox/warcproxy.py
+++ b/warcprox/warcproxy.py
@@ -36,6 +36,7 @@ from certauth.certauth import CertificateAuthority
 import warcprox
 import datetime
 import concurrent.futures
+import resource
 
 class ProxyingRecorder(object):
     """
@@ -394,12 +395,25 @@ class SingleThreadedWarcProxy(http_server.HTTPServer):
 
 class PooledMixIn(socketserver.ThreadingMixIn):
     def process_request(self, request, client_address):
-        if hasattr(self, 'pool') and self.pool:
-            self.pool.submit(self.process_request_thread, request, client_address)
-        else:
-            socketserver.ThreadingMixIn.process_request(self, request, client_address)
+        self.pool.submit(self.process_request_thread, request, client_address)
 
 class WarcProxy(PooledMixIn, SingleThreadedWarcProxy):
+    logger = logging.getLogger("warcprox.warcproxy.WarcProxy")
+
     def __init__(self, *args, **kwargs):
         SingleThreadedWarcProxy.__init__(self, *args, **kwargs)
-        self.pool = concurrent.futures.ThreadPoolExecutor(max_workers=self.options.max_threads or 500)
+        if self.options.max_threads:
+            max_threads = self.options.max_threads
+            self.logger.info("max_threads=%s set by command line option",
+                             max_threads)
+        else:
+            # man getrlimit: "RLIMIT_NPROC The maximum number of processes (or,
+            # more precisely on Linux, threads) that can be created for the
+            # real user ID of the calling process."
+            rlimit_nproc = resource.getrlimit(resource.RLIMIT_NPROC)[0]
+            rlimit_nofile = resource.getrlimit(resource.RLIMIT_NOFILE)[0]
+            max_threads = min(rlimit_nofile // 10, rlimit_nproc // 2)
+            self.logger.info("max_threads=%s (rlimit_nproc=%s, rlimit_nofile=%s)",
+                             max_threads, rlimit_nproc, rlimit_nofile)
+
+        self.pool = concurrent.futures.ThreadPoolExecutor(max_threads)