diff --git a/tools/releasetools/apex_utils.py b/tools/releasetools/apex_utils.py
index 3d16d30..113f78b 100644
--- a/tools/releasetools/apex_utils.py
+++ b/tools/releasetools/apex_utils.py
@@ -124,8 +124,9 @@
 
     android_jar_path = common.OPTIONS.android_jar_path
     if not android_jar_path:
-      android_jar_path = os.path.join(os.environ.get(
-          'ANDROID_BUILD_TOP'), 'prebuilts/sdk/current/public/android.jar')
+      android_jar_path = os.path.join(os.environ.get('ANDROID_BUILD_TOP', ''),
+                                      'prebuilts', 'sdk', 'current', 'public',
+                                      'android.jar')
       logger.warning('android_jar_path not found in options, falling back to'
                      ' use %s', android_jar_path)