1 files changed, 2 insertions, 2 deletions

diff --git a/src/mailbox.c b/src/mailbox.c
index eaf0955..aacb747 100644
--- a/src/mailbox.c
+++ b/src/mailbox.c
@@ -21,7 +21,7 @@ static inline const void* msg_data(Message msg) {
   return (const void*)((uintptr_t)(msg >> 4));
 }
 
-static inline Message msg_make(uint8_t channel, const void* data) {
+static inline Message msg_make(uint8_t channel, volatile const void* data) {
   return ((uintptr_t)(data) << 4) | (channel & 0xf);
 }
 
@@ -64,7 +64,7 @@ const Mail* mbox_read(uint8_t channel) {
   return (const Mail*)(msg_data(msg));
 }
 
-void mbox_write(uint8_t channel, const void* mail) {
+void mbox_write(uint8_t channel, volatile const void* mail) {
   // Wait until the outbox is clear.
   while (outbox_full(pMailbox));
   // Send the mail.