ys/amd64/amd64/efirt_support.S
index 98063ad561aa..54578f573750 100644
--- a/sys/amd64/amd64/efirt_support.S
+++ b/sys/amd64/amd64/efirt_support.S
@@ -58,6 +58,7 @@ ENTRY(efi_rt_arch_call)
 	cmovbl	%eax, %ecx
 	shll	$3, %ecx
 	subq	%rcx, %rsp
+	andq	$~0xf, %rsp
 
 	cmpl	$0, %ebx
 	jz	1f