diff --git a/tools/releasetools/merge_target_files.py b/tools/releasetools/merge_target_files.py
index 1af532d..689e095 100755
--- a/tools/releasetools/merge_target_files.py
+++ b/tools/releasetools/merge_target_files.py
@@ -80,6 +80,7 @@
 import logging
 import os
 import shutil
+import subprocess
 import sys
 import zipfile