diff --git a/tools/releasetools/add_img_to_target_files.py b/tools/releasetools/add_img_to_target_files.py
index 9a9fba1..7143775 100644
--- a/tools/releasetools/add_img_to_target_files.py
+++ b/tools/releasetools/add_img_to_target_files.py
@@ -170,16 +170,16 @@
     return img.name
 
   def output_sink(fn, data):
-    ofile = open(os.path.join(OPTIONS.input_tmp, "VENDOR", fn), "w")
-    ofile.write(data)
-    ofile.close()
+    output_file = os.path.join(OPTIONS.input_tmp, "VENDOR", fn)
+    with open(output_file, "wb") as ofile:
+      ofile.write(data)
 
     if output_zip:
       arc_name = "VENDOR/" + fn
       if arc_name in output_zip.namelist():
         OPTIONS.replace_updated_files_list.append(arc_name)
       else:
-        common.ZipWrite(output_zip, ofile.name, arc_name)
+        common.ZipWrite(output_zip, output_file, arc_name)
 
   board_uses_vendorimage = OPTIONS.info_dict.get(
       "board_uses_vendorimage") == "true"