diff --git a/cookbook/c04/p16_iterate_while.py b/cookbook/c04/p16_iterate_while.py
index bf140ee..c0300fc 100644
--- a/cookbook/c04/p16_iterate_while.py
+++ b/cookbook/c04/p16_iterate_while.py
@@ -22,11 +22,10 @@ def reader2(s, size):
 
 def iterate_while():
     CHUNKSIZE = 8192
-    f = open('/etc/passwd')
-    for chunk in iter(lambda: f.read(10), ''):
-        n = sys.stdout.write(chunk)
+    with open('/etc/passwd') as f:
+        for chunk in iter(lambda: f.read(10), ''):
+            n = sys.stdout.write(chunk)
 
 
 if __name__ == '__main__':
     iterate_while()
-