diff --git a/neutron/agent/linux/daemon.py b/neutron/agent/linux/daemon.py
index 7ad4ca7b37b..6ad9ee3c8b4 100644
--- a/neutron/agent/linux/daemon.py
+++ b/neutron/agent/linux/daemon.py
@@ -136,7 +136,7 @@ class Pidfile(object):
 
     def write(self, pid):
         os.ftruncate(self.fd, 0)
-        os.write(self.fd, "%d" % pid)
+        os.write(self.fd, b"%d" % pid)
         os.fsync(self.fd)
 
     def read(self):
diff --git a/neutron/tests/unit/agent/linux/test_daemon.py b/neutron/tests/unit/agent/linux/test_daemon.py
index c093909f05a..91725a648bb 100644
--- a/neutron/tests/unit/agent/linux/test_daemon.py
+++ b/neutron/tests/unit/agent/linux/test_daemon.py
@@ -180,7 +180,7 @@ class TestPidfile(base.BaseTestCase):
 
         self.os.assert_has_calls([
             mock.call.ftruncate(FAKE_FD, 0),
-            mock.call.write(FAKE_FD, '34'),
+            mock.call.write(FAKE_FD, b'34'),
             mock.call.fsync(FAKE_FD)]
         )