diff --git a/tools/releasetools/add_img_to_target_files.py b/tools/releasetools/add_img_to_target_files.py
index 4156c8b..ebaa867 100755
--- a/tools/releasetools/add_img_to_target_files.py
+++ b/tools/releasetools/add_img_to_target_files.py
@@ -28,7 +28,8 @@
 
   -r  (--rebuild_recovery)
       Rebuild the recovery patch and write it to the system image. Only
-      meaningful when system image needs to be rebuilt.
+      meaningful when system image needs to be rebuilt and there're separate
+      boot / recovery images.
 
   --replace_verity_private_key
       Replace the private key used for verity signing. (same as the option
@@ -164,7 +165,8 @@
       else:
         common.ZipWrite(output_zip, ofile.name, arc_name)
 
-  if OPTIONS.rebuild_recovery:
+  if (OPTIONS.rebuild_recovery and recovery_img is not None and
+      boot_img is not None):
     logger.info("Building new recovery patch")
     common.MakeRecoveryPatch(OPTIONS.input_tmp, output_sink, recovery_img,
                              boot_img, info_dict=OPTIONS.info_dict)