diff --git a/gunicorn/pidfile.py b/gunicorn/pidfile.py
index c8fa4c4e..32a9ac37 100644
--- a/gunicorn/pidfile.py
+++ b/gunicorn/pidfile.py
@@ -36,7 +36,7 @@ class Pidfile(object):
         if fdir and not os.path.isdir(fdir):
             raise RuntimeError("%s doesn't exist. Can't create pidfile." % fdir)
         fd, fname = tempfile.mkstemp(dir=fdir)
-        os.write(fd, "%s\n" % self.pid)
+        os.write(fd, ("%s\n" % self.pid).encode('utf-8'))
         if self.fname:
             os.rename(fname, self.fname)
         else: