diff --git a/pytest-server-fixtures/pytest_server_fixtures/xvfb.py b/pytest-server-fixtures/pytest_server_fixtures/xvfb.py
index 01d858b..58554c6 100644
--- a/pytest-server-fixtures/pytest_server_fixtures/xvfb.py
+++ b/pytest-server-fixtures/pytest_server_fixtures/xvfb.py
@@ -43,7 +43,10 @@ class XvfbServer(object):
 
     def __init__(self):
         tmpdir = mkdtemp(prefix='XvfbServer.', dir=Workspace.get_base_tempdir())
-        for servernum in range(os.getpid(), 65536):
+        pid_max = 65536
+        with open('/proc/sys/kernel/pid_max') as pid_max_file:
+            pid_max = int(pid_max_file.read())
+        for servernum in range(os.getpid(), pid_max):
             if os.path.exists('/tmp/.X{0}-lock'.format(servernum)):
                 continue
             self.display = ':' + str(servernum)
diff --git a/pytest-server-fixtures/tests/integration/test_xvfb_server.py b/pytest-server-fixtures/tests/integration/test_xvfb_server.py
index 96d6315..8ca6424 100644
--- a/pytest-server-fixtures/tests/integration/test_xvfb_server.py
+++ b/pytest-server-fixtures/tests/integration/test_xvfb_server.py
@@ -5,7 +5,7 @@
 from itertools import chain, repeat
 
 try:
-    from unittest.mock import patch
+    from unittest.mock import mock_open, patch
 except ImportError:
     # python 2
     from mock import patch
@@ -69,3 +69,23 @@ def test_handles_unexpected_failure_to_start():
         with raises(RuntimeError) as ex:
             XvfbServer()
         assert 'Failed to start Xvfb' in str(ex)
+
+
+def test_handles_64_bit_pids():
+    with patch('os.getpid') as mock_getpid:
+        # This just has to be larger than 65535
+        mock_getpid.return_value = 65537
+        with XvfbServer() as server:
+            assert server.display
+
+
+def test_errors_64_bit_pids():
+    with patch('os.getpid') as mock_getpid:
+        target = 'pytest_server_fixtures.xvfb.open'
+        with patch(target, mock_open(read_data='4')) as m:
+            # This just has to be larger than the returned max PID
+            mock_getpid.return_value = 7
+            with raises(RuntimeError) as ex:
+                XvfbServer()
+    m.assert_called_once_with('/proc/sys/kernel/pid_max')
+    assert 'Unable to find a free server number to start Xvfb' in str(ex)