diff --git a/ryu/cmd/manager.py b/ryu/cmd/manager.py
index cdcc7ae9..66d59b3b 100755
--- a/ryu/cmd/manager.py
+++ b/ryu/cmd/manager.py
@@ -17,7 +17,7 @@
 # limitations under the License.
 
 from ryu.lib import hub
-hub.patch()
+hub.patch(thread=False)
 
 # TODO:
 #   Right now, we have our own patched copy of ovs python bindings
@@ -50,6 +50,9 @@ CONF.register_cli_opts([
     cfg.MultiStrOpt('app', positional=True, default=[],
                     help='application module name to run'),
     cfg.StrOpt('pid-file', default=None, help='pid file name'),
+    cfg.BoolOpt('enable-debugger', default=False,
+                help='don\'t overwrite Python standard threading library'
+                '(use only for debugging)'),
 ])
 
 
@@ -64,6 +67,13 @@ def main(args=None, prog=None):
 
     log.init_log()
 
+    if CONF.enable_debugger:
+        LOG = logging.getLogger('ryu.cmd.manager')
+        msg = 'debugging is available (--enable-debugger option is turned on)'
+        LOG.info(msg)
+    else:
+        hub.patch(thread=True)
+
     if CONF.pid_file:
         import os
         with open(CONF.pid_file, 'w') as pid_file: