diff --git a/tools/stats/grouping.py b/tools/stats/grouping.py
index c2ecde15e43..a003219217e 100644
--- a/tools/stats/grouping.py
+++ b/tools/stats/grouping.py
@@ -72,7 +72,7 @@ def main():
     except Exception:
         stop_err("Group column not specified.")
 
-    tmpfile = tempfile.NamedTemporaryFile()
+    tmpfile = tempfile.NamedTemporaryFile(mode='r')
 
     try:
         """