diff --git a/photon/libc/sys/magenta/machine/x86_64/crt0.s b/photon/libc/sys/magenta/machine/x86_64/crt0.s
index 4261e9a..90e0b6d 100644
--- a/photon/libc/sys/magenta/machine/x86_64/crt0.s
+++ b/photon/libc/sys/magenta/machine/x86_64/crt0.s
@@ -11,7 +11,7 @@ _start:
     mov %rsp, %rsi
     andq $-16, %rsp
     call __crt_init
-    movq %rax, %rdi
-    movq $2, %rsi
-    movq $1, %rax
+    movq %rax, %rsi
+    movq $1, %rdi /* MX_EXIT_ALL_THREADS */
+    movq $1, %rax /* mx_exit() */
     syscall