diff --git a/client/cros/crash_test.py b/client/cros/crash_test.py
index fe4c75e..e7a314c 100644
--- a/client/cros/crash_test.py
+++ b/client/cros/crash_test.py
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import logging, os, re, shutil
+import contextlib, fcntl, logging, os, re, shutil
 
 import common, cros_logging
 from autotest_lib.client.bin import test, utils
@@ -74,6 +74,7 @@
     _CRASH_SENDER_PATH = '/sbin/crash_sender'
     _CRASH_SENDER_RATE_DIR = '/var/lib/crash_sender'
     _CRASH_SENDER_RUN_PATH = '/var/run/crash_sender.pid'
+    _CRASH_SENDER_LOCK_PATH = '/var/lock/crash_sender'
     _CRASH_TEST_IN_PROGRESS = '/tmp/crash-test-in-progress'
     _MOCK_CRASH_SENDING = '/tmp/mock-crash-sending'
     _PAUSE_FILE = '/var/lib/crash_sender_paused'
@@ -612,6 +613,17 @@
         self._replace_crash_reporter_filter_in('')
 
 
+    @contextlib.contextmanager
+    def hold_crash_lock(self):
+        """A context manager to hold the crash sender lock."""
+        with open(self._CRASH_SENDER_LOCK_PATH, 'w+') as f:
+            fcntl.flock(f.fileno(), fcntl.LOCK_EX)
+            try:
+                yield
+            finally:
+                fcntl.flock(f.fileno(), fcntl.LOCK_UN)
+
+
     def initialize(self):
         """Initalize the test."""
         test.test.initialize(self)
diff --git a/client/site_tests/logging_CrashSender/logging_CrashSender.py b/client/site_tests/logging_CrashSender/logging_CrashSender.py
index 284a6c4..aa38550 100644
--- a/client/site_tests/logging_CrashSender/logging_CrashSender.py
+++ b/client/site_tests/logging_CrashSender/logging_CrashSender.py
@@ -183,17 +183,12 @@
 
 
     def _test_sender_single_instance(self):
-        """Test the sender fails to start when another instance is running.
-
-        Here we rely on the sender not checking the other running pid
-        is of the same instance.
-        """
-        utils.open_write_close(self._CRASH_SENDER_RUN_PATH, str(os.getpid()))
-        result = self._call_sender_one_crash()
-        if (not 'Already running.' in result['output'] or
-            result['send_attempt'] or not result['report_exists']):
-            raise error.TestFail('Allowed multiple instances to run')
-        os.remove(self._CRASH_SENDER_RUN_PATH)
+        """Test the sender fails to start when another instance is running."""
+        with self.hold_crash_lock():
+            result = self._call_sender_one_crash()
+            if (not 'Already running; quitting.' in result['output'] or
+                result['send_attempt'] or not result['report_exists']):
+                raise error.TestFail('Allowed multiple instances to run')
 
 
     def _test_sender_send_fails(self):