diff --git a/ChangeLog b/ChangeLog
index 23c288e..74b9247 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2009-07-28  Vladimir Serbinenko  <address@hidden>
 
+	* partmap/pc.c (pc_partition_map_iterate): Check that boot flags are
+	valid.
+
+2009-07-28  Vladimir Serbinenko  <address@hidden>
+
 	* loader/i386/multiboot_helper.S (grub_multiboot_backward_relocator):
 	Clear direction flag before jumping to OS.
 	(grub_multiboot2_real_boot): Likewise.
diff --git a/partmap/pc.c b/partmap/pc.c
index 6f68ecf..6a2efd2 100644
--- a/partmap/pc.c
+++ b/partmap/pc.c
@@ -121,6 +121,10 @@ pc_partition_map_iterate (grub_disk_t disk,
       if (mbr.signature != grub_cpu_to_le16 (GRUB_PC_PARTITION_SIGNATURE))
 	return grub_error (GRUB_ERR_BAD_PART_TABLE, "no signature");
 
+      for (i = 0; i < 4; i++)
+	if (mbr.entries[i].flag & 0x7f)
+	  return grub_error (GRUB_ERR_BAD_PART_TABLE, "bad boot flag");
+
       /* Analyze DOS partitions.  */
       for (p.index = 0; p.index < 4; p.index++)
 	{