Index: mpn/x86_64/x86_64-defs.m4
--- mpn/x86_64/x86_64-defs.m4.orig
+++ mpn/x86_64/x86_64-defs.m4
@@ -95,6 +95,7 @@ m4_assert_numargs(1)
 	TYPE($1,`function')
 	COFF_TYPE($1)
 $1:
+	endbr64
 ')
 
 
