diff --git a/os/rt/include/chmboxes.h b/os/rt/include/chmboxes.h
index 7194dae46..357ee89c9 100644
--- a/os/rt/include/chmboxes.h
+++ b/os/rt/include/chmboxes.h
@@ -110,6 +110,7 @@ extern "C" {
 #endif
   void chMBObjectInit(mailbox_t *mbp, msg_t *buf, cnt_t n);
   void chMBReset(mailbox_t *mbp);
+  void chMBResetI(mailbox_t *mbp);
   msg_t chMBPost(mailbox_t *mbp, msg_t msg, systime_t timeout);
   msg_t chMBPostS(mailbox_t *mbp, msg_t msg, systime_t timeout);
   msg_t chMBPostI(mailbox_t *mbp, msg_t msg);
diff --git a/os/rt/src/chmboxes.c b/os/rt/src/chmboxes.c
index 31a5e5970..b7ae4f7d1 100644
--- a/os/rt/src/chmboxes.c
+++ b/os/rt/src/chmboxes.c
@@ -105,14 +105,29 @@ void chMBObjectInit(mailbox_t *mbp, msg_t *buf, cnt_t n) {
  */
 void chMBReset(mailbox_t *mbp) {
 
+  chSysLock();
+  chMBResetI(mbp);
+  chSchRescheduleS();
+  chSysUnlock();
+}
+
+/**
+ * @brief   Resets a @p mailbox_t object.
+ * @details All the waiting threads are resumed with status @p MSG_RESET and
+ *          the queued messages are lost.
+ *
+ * @param[in] mbp       the pointer to an initialized @p mailbox_t object
+ *
+ * @api
+ */
+void chMBResetI(mailbox_t *mbp) {
+
+  chDbgCheckClassI();
   chDbgCheck(mbp != NULL);
 
-  chSysLock();
   mbp->mb_wrptr = mbp->mb_rdptr = mbp->mb_buffer;
   chSemResetI(&mbp->mb_emptysem, mbp->mb_top - mbp->mb_buffer);
   chSemResetI(&mbp->mb_fullsem, 0);
-  chSchRescheduleS();
-  chSysUnlock();
 }
 
 /**