diff --git a/tools/releasetools/build_image.py b/tools/releasetools/build_image.py
index e6ad18b821..e248860d3d 100755
--- a/tools/releasetools/build_image.py
+++ b/tools/releasetools/build_image.py
@@ -28,6 +28,7 @@ import sys
 import commands
 import common
 import shutil
+import sparse_img
 import tempfile
 
 OPTIONS = common.OPTIONS
@@ -91,6 +92,16 @@ def GetVeritySize(partition_size, fec_supported):
     return verity_size + fec_size
   return verity_size
 
+def GetSimgSize(image_file):
+  simg = sparse_img.SparseImage(image_file, build_map=False)
+  return simg.blocksize * simg.total_blocks
+
+def ZeroPadSimg(image_file, pad_size):
+  blocks = pad_size // BLOCK_SIZE
+  print("Padding %d blocks (%d bytes)" % (blocks, pad_size))
+  simg = sparse_img.SparseImage(image_file, mode="r+b", build_map=False)
+  simg.AppendFillChunk(0, blocks)
+
 def AdjustPartitionSizeForVerity(partition_size, fec_supported):
   """Modifies the provided partition size to account for the verity metadata.
 
@@ -329,7 +340,7 @@ def BuildImage(in_dir, prop_dict, out_file, target_out=None):
 
   # Adjust the partition size to make room for the hashes if this is to be
   # verified.
-  if verity_supported and is_verity_partition and fs_spans_partition:
+  if verity_supported and is_verity_partition:
     partition_size = int(prop_dict.get("partition_size"))
     adjusted_size = AdjustPartitionSizeForVerity(partition_size,
                                                  verity_fec_supported)
@@ -440,17 +451,13 @@ def BuildImage(in_dir, prop_dict, out_file, target_out=None):
   if not fs_spans_partition:
     mount_point = prop_dict.get("mount_point")
     partition_size = int(prop_dict.get("partition_size"))
-    image_size = os.stat(out_file).st_size
+    image_size = GetSimgSize(out_file)
     if image_size > partition_size:
       print("Error: %s image size of %d is larger than partition size of "
             "%d" % (mount_point, image_size, partition_size))
       return False
     if verity_supported and is_verity_partition:
-      if 2 * image_size - AdjustPartitionSizeForVerity(image_size, verity_fec_supported) > partition_size:
-        print "Error: No more room on %s to fit verity data" % mount_point
-        return False
-    prop_dict["original_partition_size"] = prop_dict["partition_size"]
-    prop_dict["partition_size"] = str(image_size)
+      ZeroPadSimg(out_file, partition_size - image_size)
 
   # create the verified image if this is to be verified
   if verity_supported and is_verity_partition:
diff --git a/tools/releasetools/sparse_img.py b/tools/releasetools/sparse_img.py
index 013044f6ff..4ba7560dfc 100644
--- a/tools/releasetools/sparse_img.py
+++ b/tools/releasetools/sparse_img.py
@@ -31,8 +31,9 @@ class SparseImage(object):
   the form of a string like "0" or "0 1-5 8".
   """
 
-  def __init__(self, simg_fn, file_map_fn=None, clobbered_blocks=None):
-    self.simg_f = f = open(simg_fn, "rb")
+  def __init__(self, simg_fn, file_map_fn=None, clobbered_blocks=None,
+               mode="rb", build_map=True):
+    self.simg_f = f = open(simg_fn, mode)
 
     header_bin = f.read(28)
     header = struct.unpack("<I4H4I", header_bin)
@@ -44,7 +45,7 @@ class SparseImage(object):
     chunk_hdr_sz = header[4]
     self.blocksize = blk_sz = header[5]
     self.total_blocks = total_blks = header[6]
-    total_chunks = header[7]
+    self.total_chunks = total_chunks = header[7]
 
     if magic != 0xED26FF3A:
       raise ValueError("Magic should be 0xED26FF3A but is 0x%08X" % (magic,))
@@ -61,6 +62,9 @@ class SparseImage(object):
     print("Total of %u %u-byte output blocks in %u input chunks."
           % (total_blks, blk_sz, total_chunks))
 
+    if not build_map:
+      return
+
     pos = 0   # in blocks
     care_data = []
     self.offset_map = offset_map = []
@@ -126,6 +130,20 @@ class SparseImage(object):
     else:
       self.file_map = {"__DATA": self.care_map}
 
+  def AppendFillChunk(self, data, blocks):
+    f = self.simg_f
+
+    # Append a fill chunk
+    f.seek(0, os.SEEK_END)
+    f.write(struct.pack("<2H3I", 0xCAC2, 0, blocks, 16, data))
+
+    # Update the sparse header
+    self.total_blocks += blocks
+    self.total_chunks += 1
+
+    f.seek(16, os.SEEK_SET)
+    f.write(struct.pack("<2I", self.total_blocks, self.total_chunks))
+
   def ReadRangeSet(self, ranges):
     return [d for d in self._GetRangeData(ranges)]