diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index bea33a3..73f7e33 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -63,6 +63,13 @@
       the build scripts (used for developer OTA packages which
       legitimately need to go back and forth).
 
+  --downgrade
+      Intentionally generate an incremental OTA that updates from a newer
+      build to an older one (based on timestamp comparison). "post-timestamp"
+      will be replaced by "ota-downgrade=yes" in the metadata file. A data
+      wipe will always be enforced, so "ota-wipe=yes" will also be included in
+      the metadata file.
+
   -e  (--extra_script)  <file>
       Insert the contents of file at the end of the update script.
 
@@ -126,6 +133,7 @@
 OPTIONS.patch_threshold = 0.95
 OPTIONS.wipe_user_data = False
 OPTIONS.omit_prereq = False
+OPTIONS.downgrade = False
 OPTIONS.extra_script = None
 OPTIONS.aslr_mode = True
 OPTIONS.worker_threads = multiprocessing.cpu_count() // 2
@@ -698,8 +706,9 @@
 endif;
 endif;
 """ % bcb_dev)
-  script.AddToZip(input_zip, output_zip, input_path=OPTIONS.updater_binary)
 
+  script.SetProgress(1)
+  script.AddToZip(input_zip, output_zip, input_path=OPTIONS.updater_binary)
   metadata["ota-required-cache"] = str(script.required_cache)
   WriteMetadata(metadata, output_zip)
 
@@ -775,11 +784,30 @@
   metadata = {
       "pre-device": GetOemProperty("ro.product.device", oem_props, oem_dict,
                                    OPTIONS.source_info_dict),
-      "post-timestamp": GetBuildProp("ro.build.date.utc",
-                                     OPTIONS.target_info_dict),
       "ota-type": "BLOCK",
   }
 
+  post_timestamp = GetBuildProp("ro.build.date.utc", OPTIONS.target_info_dict)
+  pre_timestamp = GetBuildProp("ro.build.date.utc", OPTIONS.source_info_dict)
+  is_downgrade = long(post_timestamp) < long(pre_timestamp)
+
+  if OPTIONS.downgrade:
+    metadata["ota-downgrade"] = "yes"
+    if not is_downgrade:
+      raise RuntimeError("--downgrade specified but no downgrade detected: "
+                         "pre: %s, post: %s" % (pre_timestamp, post_timestamp))
+  else:
+    if is_downgrade:
+      # Non-fatal here to allow generating such a package which may require
+      # manual work to adjust the post-timestamp. A legit use case is that we
+      # cut a new build C (after having A and B), but want to enfore the
+      # update path of A -> C -> B. Specifying --downgrade may not help since
+      # that would enforce a data wipe for C -> B update.
+      print("\nWARNING: downgrade detected: pre: %s, post: %s.\n"
+            "The package may not be deployed properly. "
+            "Try --downgrade?\n" % (pre_timestamp, post_timestamp))
+    metadata["post-timestamp"] = post_timestamp
+
   device_specific = common.DeviceSpecificParams(
       source_zip=source_zip,
       source_version=source_version,
@@ -1009,6 +1037,7 @@
   if OPTIONS.wipe_user_data:
     script.Print("Erasing user data...")
     script.FormatPartition("/data")
+    metadata["ota-wipe"] = "yes"
 
   if OPTIONS.two_step:
     script.AppendExtra("""
@@ -1392,11 +1421,30 @@
   metadata = {
       "pre-device": GetOemProperty("ro.product.device", oem_props, oem_dict,
                                    OPTIONS.source_info_dict),
-      "post-timestamp": GetBuildProp("ro.build.date.utc",
-                                     OPTIONS.target_info_dict),
       "ota-type": "FILE",
   }
 
+  post_timestamp = GetBuildProp("ro.build.date.utc", OPTIONS.target_info_dict)
+  pre_timestamp = GetBuildProp("ro.build.date.utc", OPTIONS.source_info_dict)
+  is_downgrade = long(post_timestamp) < long(pre_timestamp)
+
+  if OPTIONS.downgrade:
+    metadata["ota-downgrade"] = "yes"
+    if not is_downgrade:
+      raise RuntimeError("--downgrade specified but no downgrade detected: "
+                         "pre: %s, post: %s" % (pre_timestamp, post_timestamp))
+  else:
+    if is_downgrade:
+      # Non-fatal here to allow generating such a package which may require
+      # manual work to adjust the post-timestamp. A legit use case is that we
+      # cut a new build C (after having A and B), but want to enfore the
+      # update path of A -> C -> B. Specifying --downgrade may not help since
+      # that would enforce a data wipe for C -> B update.
+      print("\nWARNING: downgrade detected: pre: %s, post: %s.\n"
+            "The package may not be deployed properly. "
+            "Try --downgrade?\n" % (pre_timestamp, post_timestamp))
+    metadata["post-timestamp"] = post_timestamp
+
   device_specific = common.DeviceSpecificParams(
       source_zip=source_zip,
       source_version=source_version,
@@ -1725,6 +1773,7 @@
   if OPTIONS.wipe_user_data:
     script.Print("Erasing user data...")
     script.FormatPartition("/data")
+    metadata["ota-wipe"] = "yes"
 
   if OPTIONS.two_step:
     script.AppendExtra("""
@@ -1767,6 +1816,9 @@
       OPTIONS.wipe_user_data = True
     elif o in ("-n", "--no_prereq"):
       OPTIONS.omit_prereq = True
+    elif o == "--downgrade":
+      OPTIONS.downgrade = True
+      OPTIONS.wipe_user_data = True
     elif o in ("-o", "--oem_settings"):
       OPTIONS.oem_source = a
     elif o in ("-e", "--extra_script"):
@@ -1818,6 +1870,7 @@
                                  "full_bootloader",
                                  "wipe_user_data",
                                  "no_prereq",
+                                 "downgrade",
                                  "extra_script=",
                                  "worker_threads=",
                                  "aslr_mode=",
@@ -1837,6 +1890,18 @@
     common.Usage(__doc__)
     sys.exit(1)
 
+  if OPTIONS.downgrade:
+    # Sanity check to enforce a data wipe.
+    if not OPTIONS.wipe_user_data:
+      raise ValueError("Cannot downgrade without a data wipe")
+
+    # We should only allow downgrading incrementals (as opposed to full).
+    # Otherwise the device may go back from arbitrary build with this full
+    # OTA package.
+    if OPTIONS.incremental_source is None:
+      raise ValueError("Cannot generate downgradable full OTAs - consider"
+                       "using --omit_prereq?")
+
   # Load the dict file from the zip directly to have a peek at the OTA type.
   # For packages using A/B update, unzipping is not needed.
   input_zip = zipfile.ZipFile(args[0], "r")