diff --git a/build/image/convert_to_binary.py b/build/image/convert_to_binary.py
index 7900cf2..bf50a8e 100644
--- a/build/image/convert_to_binary.py
+++ b/build/image/convert_to_binary.py
@@ -6,7 +6,6 @@
 """
 
 import argparse
-import os
 import subprocess
 import sys
 
@@ -16,7 +15,7 @@
   parser.add_argument("--input", required=True)
   parser.add_argument("--output", required=True)
   args = parser.parse_args()
-  raw = subprocess.check_output([
+  subprocess.check_call([
       "{}objcopy".format(args.tool_prefix),
       "-O",
       "binary",