diff --git a/Lib/mailbox.py b/Lib/mailbox.py
index 108d874..f9af494 100755
--- a/Lib/mailbox.py
+++ b/Lib/mailbox.py
@@ -1887,7 +1887,8 @@
 def _sync_flush(f):
     """Ensure changes to file f are physically on disk."""
     f.flush()
-    os.fsync(f.fileno())
+    if hasattr(os, 'fsync'):
+        os.fsync(f.fileno())
 
 def _sync_close(f):
     """Close file f, ensuring all changes are physically on disk."""