diff --git a/Lib/test/test_posix.py b/Lib/test/test_posix.py
index 4f6abc6f7d6fd93..6942ded1e6adc91 100644
--- a/Lib/test/test_posix.py
+++ b/Lib/test/test_posix.py
@@ -1527,8 +1527,10 @@ def test_open_file(self):
         outfile = support.TESTFN
         self.addCleanup(support.unlink, outfile)
         script = """if 1:
-            import sys
+            import sys, os
             sys.stdout.write("hello")
+            sys.stdout.flush()
+            os.fsync(sys.stdout.fileno())
             """
         file_actions = [
             (os.POSIX_SPAWN_OPEN, 1, outfile,