diff --git a/firmware/include/vboot_struct.h b/firmware/include/vboot_struct.h
index 6be7256aca..08910d1316 100644
--- a/firmware/include/vboot_struct.h
+++ b/firmware/include/vboot_struct.h
@@ -176,7 +176,9 @@ typedef struct VbKernelPreambleHeader {
 	 * Flags passed in by the signer. Readers should return 0 for header
 	 * version < 2.2. Flags field is currently defined as:
 	 * [31:2] - Reserved (for future use)
-	 * [1:0]  - Kernel image type (0b00 - CrOS, 0b01 - bootimg)
+	 * [1:0]  - Kernel image type (0b00 - CrOS,
+	 *                             0b01 - bootimg,
+	 *                             0b10 - multiboot)
 	 */
 	uint32_t flags;
 } __attribute__((packed)) VbKernelPreambleHeader;
diff --git a/firmware/lib20/include/vb2_struct.h b/firmware/lib20/include/vb2_struct.h
index 4f5d9995ad..b409376a22 100644
--- a/firmware/lib20/include/vb2_struct.h
+++ b/firmware/lib20/include/vb2_struct.h
@@ -192,9 +192,10 @@ struct vb2_fw_preamble {
 /* Flags for vb2_kernel_preamble.flags */
 /* Kernel image type = bits 1:0 */
 #define VB2_KERNEL_PREAMBLE_KERNEL_TYPE_MASK 0x00000003
-#define VB2_KERNEL_PREAMBLE_KERNEL_TYPE_CROS    0
-#define VB2_KERNEL_PREAMBLE_KERNEL_TYPE_BOOTIMG 1
-/* Kernel types 2,3 are reserved for future use */
+#define VB2_KERNEL_PREAMBLE_KERNEL_TYPE_CROS      0
+#define VB2_KERNEL_PREAMBLE_KERNEL_TYPE_BOOTIMG   1
+#define VB2_KERNEL_PREAMBLE_KERNEL_TYPE_MULTIBOOT 2
+/* Kernel type 3 is reserved for future use */
 
 /*
  * Preamble block for kernel, version 2.2