diff --git a/tools/releasetools/build_image.py b/tools/releasetools/build_image.py
index 6d22694..0aeadaf 100755
--- a/tools/releasetools/build_image.py
+++ b/tools/releasetools/build_image.py
@@ -281,7 +281,7 @@
         logger.info(
             "Not worth reducing image %d <= %d.", free_size, reserved_size)
       else:
-        size -= free_size + (free_size // 60)
+        size -= free_size + (free_size // 61)
         size += reserved_size
         if block_size <= 4096:
           size = common.RoundUpTo4K(size)