diff --git a/tests/test_writer.py b/tests/test_writer.py
index 8aedc7d..444909f 100644
--- a/tests/test_writer.py
+++ b/tests/test_writer.py
@@ -24,7 +24,7 @@ def lock_file(queue, filename):
     """
     try:
         fi = open(filename, 'ab')
-        fcntl.flock(fi, fcntl.LOCK_EX | fcntl.LOCK_NB)
+        fcntl.lockf(fi, fcntl.LOCK_EX | fcntl.LOCK_NB)
         fi.close()
         queue.put('1')
     except IOError:
diff --git a/warcprox/writer.py b/warcprox/writer.py
index a3e24c6..7a1032a 100644
--- a/warcprox/writer.py
+++ b/warcprox/writer.py
@@ -74,7 +74,7 @@ class WarcWriter:
                 self.logger.info('closing %s', self._f_finalname)
                 if self._f_open_suffix == '':
                     try:
-                        fcntl.flock(self._f, fcntl.LOCK_UN)
+                        fcntl.lockf(self._f, fcntl.LOCK_UN)
                     except IOError as exc:
                         self.logger.error('could not unlock file %s (%s)',
                                           self._fpath, exc)
@@ -106,7 +106,7 @@ class WarcWriter:
                 # file lock.
                 if self._f_open_suffix == '':
                     try:
-                        fcntl.flock(self._f, fcntl.LOCK_EX | fcntl.LOCK_NB)
+                        fcntl.lockf(self._f, fcntl.LOCK_EX | fcntl.LOCK_NB)
                     except IOError as exc:
                         self.logger.error('could not lock file %s (%s)',
                                           self._fpath, exc)