diff --git a/arch/x86_64/src/common/multiboot1.S b/arch/x86_64/src/common/multiboot1.S
index 36365b86f21..9d0ba73bc0f 100644
--- a/arch/x86_64/src/common/multiboot1.S
+++ b/arch/x86_64/src/common/multiboot1.S
@@ -54,15 +54,9 @@ _start:
     movl                $realmode_start, %esi
     movl                $0, %edi
 
-copy_loop:
-
     /* Copy by bytes, make sure the addresses are not overlapped */
-
-    movb                (%esi), %al
-    movb                %al, (%edi)
-    inc                 %esi
-    inc                 %edi
-    loop                copy_loop
+    cld
+    rep movsb
 
     /* Jump to bin_start + 0x30, skip the multiboot1 header */