diff --git a/build_library/disk_util b/build_library/disk_util
index 9c400c1cab..0e79976860 100755
--- a/build_library/disk_util
+++ b/build_library/disk_util
@@ -420,7 +420,7 @@ def FormatFat(part, device):
   vfat_block_size = 1024
   vfat_blocks = part['bytes'] // vfat_block_size
 
-  cmd = ['mkfs.vfat']
+  cmd = ['mkfs.vfat', '-I']
   if 'fs_label' in part:
     cmd += ['-n', part['fs_label']]
   if part['type'] == 'efi':