diff --git a/Lib/test/test_mmap.py b/Lib/test/test_mmap.py
index fcf3c92ca75..4fb4ec10c50 100644
--- a/Lib/test/test_mmap.py
+++ b/Lib/test/test_mmap.py
@@ -17,7 +17,7 @@ def test_both():
         f.write('\0'* PAGESIZE)
         f.write('foo')
         f.write('\0'* (PAGESIZE-3) )
-
+        f.flush()
         m = mmap.mmap(f.fileno(), 2 * PAGESIZE)
         f.close()