diff --git a/util/cbfstool/cbfs.h b/util/cbfstool/cbfs.h
index 14a7a37..6286eff 100644
--- a/util/cbfstool/cbfs.h
+++ b/util/cbfstool/cbfs.h
@@ -71,12 +71,16 @@
 
 struct cbfs_file {
 	uint8_t magic[8];
+	/* length of file data */
 	uint32_t len;
 	uint32_t type;
 	uint32_t checksum;
+	/* length of header incl. variable data */
 	uint32_t offset;
 } __PACKED;
 
+_Static_assert(sizeof(struct cbfs_file) == 24, "cbfs_file size mismatch");
+
 struct cbfs_stage {
 	uint32_t compression;
 	uint64_t entry;