diff --git a/virttest/cartesian_config.py b/virttest/cartesian_config.py
index 39fcb279a3..ca8589c05d 100755
--- a/virttest/cartesian_config.py
+++ b/virttest/cartesian_config.py
@@ -441,7 +441,8 @@ def __init__(self, filename):
 
         :parse filename: The name of the input file.
         """
-        StrReader.__init__(self, open(filename).read())
+        with open(filename) as f:
+            StrReader.__init__(self, f.read())
         self.filename = filename