diff --git a/soc/runtime/mailbox.c b/soc/runtime/mailbox.c
index df0960302..1ed0f4c33 100644
--- a/soc/runtime/mailbox.c
+++ b/soc/runtime/mailbox.c
@@ -2,10 +2,11 @@
 #include <system.h>
 #include <spr-defs.h>
 #include <hw/common.h>
+#include <generated/mem.h>
 
 #include "mailbox.h"
 
-#define KERNELCPU_MAILBOX MMPTR(0xf0000000)
+#define KERNELCPU_MAILBOX MMPTR(MAILBOX_BASE)
 
 static unsigned int last_transmission;
 
diff --git a/soc/targets/artiq_kc705.py b/soc/targets/artiq_kc705.py
index 40ceed001..9d3ee331c 100644
--- a/soc/targets/artiq_kc705.py
+++ b/soc/targets/artiq_kc705.py
@@ -125,6 +125,7 @@ class AMP(_Peripherals):
         self.submodules.mailbox = amp.Mailbox()
         self.add_wb_slave(mem_decoder(self.mem_map["mailbox"]), self.mailbox.i1)
         self.kernel_cpu.add_wb_slave(mem_decoder(self.mem_map["mailbox"]), self.mailbox.i2)
+        self.add_memory_region("mailbox", self.mem_map["mailbox"] + 0x80000000, 4)
 
         rtio_csrs = self.rtio.get_kernel_csrs()
         self.submodules.rtiowb = wbgen.Bank(rtio_csrs)