diff --git a/stand/efi/libefi/efipart.c b/stand/efi/libefi/efipart.c
index a5a1a8220604..3193cd5ab43e 100644
--- a/stand/efi/libefi/efipart.c
+++ b/stand/efi/libefi/efipart.c
@@ -260,6 +260,8 @@ efipart_hdd(EFI_DEVICE_PATH *dp)
 
 		/*
 		 * We assume the block size 512 or greater power of 2. 
+		 * iPXE is known to insert stub BLOCK IO device with
+		 * BlockSize 1.
 		 */
 		if (blkio->Media->BlockSize < 512 ||
 		    !powerof2(blkio->Media->BlockSize)) {