diff --git a/tools/releasetools/build_image.py b/tools/releasetools/build_image.py
index 8a5d627..34aa1a6 100755
--- a/tools/releasetools/build_image.py
+++ b/tools/releasetools/build_image.py
@@ -651,6 +651,10 @@
   if not mkfs_output:
     mkfs_output = BuildImageMkfs(in_dir, prop_dict, out_file, target_out, fs_config)
 
+  # Update the image (eg filesystem size). This can be different eg if mkfs
+  # rounds the requested size down due to alignment.
+  prop_dict["image_size"] = common.sparse_img.GetImagePartitionSize(out_file)
+
   # Check if there's enough headroom space available for ext4 image.
   if "partition_headroom" in prop_dict and fs_type.startswith("ext4"):
     CheckHeadroom(mkfs_output, prop_dict)