diff --git a/src/interface/efi/efi_init.c b/src/interface/efi/efi_init.c
index 284c39b..e1041a5 100644
--- a/src/interface/efi/efi_init.c
+++ b/src/interface/efi/efi_init.c
@@ -21,6 +21,7 @@
 
 #include <string.h>
 #include <errno.h>
+#include <endian.h>
 #include <ipxe/init.h>
 #include <ipxe/rotate.h>
 #include <ipxe/efi/efi.h>
@@ -128,6 +129,13 @@
 	 */
 	cookie <<= 8;
 
+	/* Ensure that the NUL byte is placed at the bottom of the
+	 * stack cookie, to avoid potential disclosure via an
+	 * unterminated string.
+	 */
+	if ( __BYTE_ORDER == __BIG_ENDIAN )
+		cookie >>= 8;
+
 	return cookie;
 }