diff --git a/scripts/update_payload/applier.py b/scripts/update_payload/applier.py
index 9582b3d..dad5ba3 100644
--- a/scripts/update_payload/applier.py
+++ b/scripts/update_payload/applier.py
@@ -622,21 +622,24 @@
       _VerifySha256(new_part_file, new_part_info.hash,
                     'new ' + part_name, length=new_part_info.size)
 
-  def Run(self, new_kernel_part, new_rootfs_part, old_kernel_part=None,
-          old_rootfs_part=None):
+  def Run(self, new_parts, old_parts=None):
     """Applier entry point, invoking all update operations.
 
     Args:
-      new_kernel_part: name of dest kernel partition file
-      new_rootfs_part: name of dest rootfs partition file
-      old_kernel_part: name of source kernel partition file (optional)
-      old_rootfs_part: name of source rootfs partition file (optional)
+      new_parts: map of partition name to dest partition file
+      old_parts: map of partition name to source partition file (optional)
 
     Raises:
       PayloadError if payload application failed.
     """
     self.payload.ResetFile()
 
+    # TODO(tbrindus): make payload applying work for major version 2 partitions
+    new_kernel_part = new_parts[common.KERNEL]
+    new_rootfs_part = new_parts[common.ROOTFS]
+    old_kernel_part = old_parts.get(common.KERNEL, None) if old_parts else None
+    old_rootfs_part = old_parts.get(common.ROOTFS, None) if old_parts else None
+
     # Make sure the arguments are sane and match the payload.
     if not (new_kernel_part and new_rootfs_part):
       raise PayloadError('missing dst {kernel,rootfs} partitions')
diff --git a/scripts/update_payload/checker.py b/scripts/update_payload/checker.py
index 49c556f..ec8810d 100644
--- a/scripts/update_payload/checker.py
+++ b/scripts/update_payload/checker.py
@@ -561,8 +561,7 @@
     Raises:
       error.PayloadError if any of the checks fail.
     """
-    if part_sizes is None:
-      part_sizes = collections.defaultdict(int)
+    part_sizes = collections.defaultdict(int, part_sizes)
 
     manifest = self.payload.manifest
     report.AddSection('manifest')
@@ -1226,17 +1225,15 @@
                                  sig.version)
 
   def Run(self, pubkey_file_name=None, metadata_sig_file=None, metadata_size=0,
-          rootfs_part_size=0, kernel_part_size=0, report_out_file=None):
+          part_sizes=None, report_out_file=None):
     """Checker entry point, invoking all checks.
 
     Args:
       pubkey_file_name: Public key used for signature verification.
       metadata_sig_file: Metadata signature, if verification is desired.
-      metadata_size: metadata size, if verification is desired
-      rootfs_part_size: The size of rootfs partitions in bytes (default: infer
-                        based on payload type and version).
-      kernel_part_size: The size of kernel partitions in bytes (default: use
-                        reported filesystem size).
+      metadata_size: Metadata size, if verification is desired.
+      part_sizes: Mapping of partition label to size in bytes (default: infer
+        based on payload type and version or filesystem).
       report_out_file: File object to dump the report to.
 
     Raises:
@@ -1276,10 +1273,7 @@
       report.AddField('manifest len', self.payload.header.manifest_len)
 
       # Part 2: Check the manifest.
-      self._CheckManifest(report, {
-          common.ROOTFS: rootfs_part_size,
-          common.KERNEL: kernel_part_size
-      })
+      self._CheckManifest(report, part_sizes)
       assert self.payload_type, 'payload type should be known by now'
 
       # Infer the usable partition size when validating rootfs operations:
@@ -1290,9 +1284,9 @@
       # - Otherwise, use the encoded filesystem size.
       new_rootfs_usable_size = self.new_fs_sizes[common.ROOTFS]
       old_rootfs_usable_size = self.old_fs_sizes[common.ROOTFS]
-      if rootfs_part_size:
-        new_rootfs_usable_size = rootfs_part_size
-        old_rootfs_usable_size = rootfs_part_size
+      if part_sizes.get(common.ROOTFS, 0):
+        new_rootfs_usable_size = part_sizes[common.ROOTFS]
+        old_rootfs_usable_size = part_sizes[common.ROOTFS]
       elif self.payload_type == _TYPE_DELTA and self.minor_version in (None, 1):
         new_rootfs_usable_size = _OLD_DELTA_USABLE_PART_SIZE
         old_rootfs_usable_size = _OLD_DELTA_USABLE_PART_SIZE
@@ -1313,6 +1307,7 @@
       report.AddSection('kernel operations')
       old_kernel_fs_size = self.old_fs_sizes[common.KERNEL]
       new_kernel_fs_size = self.new_fs_sizes[common.KERNEL]
+      kernel_part_size = part_sizes.get(common.KERNEL, None)
       total_blob_size += self._CheckOperations(
           self.payload.manifest.kernel_install_operations, report,
           'kernel_install_operations', old_kernel_fs_size, new_kernel_fs_size,
diff --git a/scripts/update_payload/checker_unittest.py b/scripts/update_payload/checker_unittest.py
index d42f4b4..ed5ee80 100755
--- a/scripts/update_payload/checker_unittest.py
+++ b/scripts/update_payload/checker_unittest.py
@@ -1205,10 +1205,13 @@
       payload_checker = _GetPayloadChecker(payload_gen.WriteToFileWithData,
                                            **kwargs)
 
-      kwargs = {'pubkey_file_name': test_utils._PUBKEY_FILE_NAME,
-                'rootfs_part_size': rootfs_part_size,
-                'metadata_size': metadata_size,
-                'kernel_part_size': kernel_part_size}
+      kwargs = {
+          'pubkey_file_name': test_utils._PUBKEY_FILE_NAME,
+          'metadata_size': metadata_size,
+          'part_sizes': {
+              common.KERNEL: kernel_part_size,
+              common.ROOTFS: rootfs_part_size}}
+
       should_fail = (fail_wrong_payload_type or fail_mismatched_block_size or
                      fail_mismatched_metadata_size or fail_excess_data or
                      fail_rootfs_part_size_exceeded or
diff --git a/scripts/update_payload/payload.py b/scripts/update_payload/payload.py
index 15f66d0..2a0cb58 100644
--- a/scripts/update_payload/payload.py
+++ b/scripts/update_payload/payload.py
@@ -274,8 +274,8 @@
 
   def Check(self, pubkey_file_name=None, metadata_sig_file=None,
             metadata_size=0, report_out_file=None, assert_type=None,
-            block_size=0, rootfs_part_size=0, kernel_part_size=0,
-            allow_unhashed=False, disabled_tests=()):
+            block_size=0, part_sizes=None, allow_unhashed=False,
+            disabled_tests=()):
     """Checks the payload integrity.
 
     Args:
@@ -285,8 +285,7 @@
       report_out_file: file object to dump the report to
       assert_type: assert that payload is either 'full' or 'delta'
       block_size: expected filesystem / payload block size
-      rootfs_part_size: the size of (physical) rootfs partitions in bytes
-      kernel_part_size: the size of (physical) kernel partitions in bytes
+      part_sizes: map of partition label to (physical) size in bytes
       allow_unhashed: allow unhashed operation blobs
       disabled_tests: list of tests to disable
 
@@ -302,20 +301,17 @@
     helper.Run(pubkey_file_name=pubkey_file_name,
                metadata_sig_file=metadata_sig_file,
                metadata_size=metadata_size,
-               rootfs_part_size=rootfs_part_size,
-               kernel_part_size=kernel_part_size,
+               part_sizes=part_sizes,
                report_out_file=report_out_file)
 
-  def Apply(self, new_kernel_part, new_rootfs_part, old_kernel_part=None,
-            old_rootfs_part=None, bsdiff_in_place=True, bspatch_path=None,
-            puffpatch_path=None, truncate_to_expected_size=True):
+  def Apply(self, new_parts, old_parts=None, bsdiff_in_place=True,
+            bspatch_path=None, puffpatch_path=None,
+            truncate_to_expected_size=True):
     """Applies the update payload.
 
     Args:
-      new_kernel_part: name of dest kernel partition file
-      new_rootfs_part: name of dest rootfs partition file
-      old_kernel_part: name of source kernel partition file (optional)
-      old_rootfs_part: name of source rootfs partition file (optional)
+      new_parts: map of partition name to dest partition file
+      old_parts: map of partition name to partition file (optional)
       bsdiff_in_place: whether to perform BSDIFF operations in-place (optional)
       bspatch_path: path to the bspatch binary (optional)
       puffpatch_path: path to the puffpatch binary (optional)
@@ -333,6 +329,4 @@
         self, bsdiff_in_place=bsdiff_in_place, bspatch_path=bspatch_path,
         puffpatch_path=puffpatch_path,
         truncate_to_expected_size=truncate_to_expected_size)
-    helper.Run(new_kernel_part, new_rootfs_part,
-               old_kernel_part=old_kernel_part,
-               old_rootfs_part=old_rootfs_part)
+    helper.Run(new_parts, old_parts=old_parts)