diff --git a/django/utils/daemonize.py b/django/utils/daemonize.py
index 763a9db752..76f4d5d082 100644
--- a/django/utils/daemonize.py
+++ b/django/utils/daemonize.py
@@ -1,6 +1,10 @@
 import os
 import sys
 
+from . import six
+
+buffering = int(six.PY3)        # No unbuffered text I/O on Python 3 (#20815).
+
 if os.name == 'posix':
     def become_daemon(our_home_dir='.', out_log='/dev/null',
                       err_log='/dev/null', umask=0o022):
@@ -25,8 +29,8 @@ if os.name == 'posix':
             os._exit(1)
 
         si = open('/dev/null', 'r')
-        so = open(out_log, 'a+', 0)
-        se = open(err_log, 'a+', 0)
+        so = open(out_log, 'a+', buffering)
+        se = open(err_log, 'a+', buffering)
         os.dup2(si.fileno(), sys.stdin.fileno())
         os.dup2(so.fileno(), sys.stdout.fileno())
         os.dup2(se.fileno(), sys.stderr.fileno())
@@ -44,11 +48,11 @@ else:
         sys.stdout.close()
         sys.stderr.close()
         if err_log:
-            sys.stderr = open(err_log, 'a', 0)
+            sys.stderr = open(err_log, 'a', buffering)
         else:
             sys.stderr = NullDevice()
         if out_log:
-            sys.stdout = open(out_log, 'a', 0)
+            sys.stdout = open(out_log, 'a', buffering)
         else:
             sys.stdout = NullDevice()