diff --git a/Lib/base64.py b/Lib/base64.py
index 41a5e14..85204dd 100755
--- a/Lib/base64.py
+++ b/Lib/base64.py
@@ -343,7 +343,8 @@
         if o == '-u': func = decode
         if o == '-t': test1(); return
     if args and args[0] != '-':
-        func(open(args[0], 'rb'), sys.stdout)
+        with open(args[0], 'rb') as f:
+            func(f, sys.stdout)
     else:
         func(sys.stdin, sys.stdout)