diff --git a/src/libty/board.c b/src/libty/board.c
index cebfbc6d..9984930e 100644
--- a/src/libty/board.c
+++ b/src/libty/board.c
@@ -12,6 +12,7 @@
 #ifndef _WIN32
     #include <sys/stat.h>
 #endif
+#include <time.h>
 #include "../libhs/device.h"
 #include "board_priv.h"
 #include "class_priv.h"
@@ -419,6 +420,25 @@ int ty_board_reboot(ty_board *board)
     return r;
 }
 
+int ty_board_set_rtc(ty_board *board, int64_t time)
+{
+    assert(board);
+
+    ty_board_interface *iface;
+    int r;
+
+    r = ty_board_open_interface(board, TY_BOARD_CAPABILITY_RTC, &iface);
+    if (r < 0)
+        return r;
+    if (!r)
+        return ty_error(TY_ERROR_MODE, "Cannot set RTC on board '%s'", board->tag);
+
+    r = (*iface->class_vtable->set_rtc)(iface, time);
+
+    ty_board_interface_close(iface);
+    return r;
+}
+
 ty_board_interface *ty_board_interface_ref(ty_board_interface *iface)
 {
     assert(iface);
@@ -651,7 +671,7 @@ static int run_upload(ty_task *task)
 
 wait:
     r = ty_board_wait_for(board, TY_BOARD_CAPABILITY_UPLOAD,
-                           flags & TY_UPLOAD_WAIT ? -1 : MANUAL_REBOOT_DELAY);
+                          flags & TY_UPLOAD_WAIT ? -1 : MANUAL_REBOOT_DELAY);
     if (r < 0)
         return r;
     if (!r) {
@@ -673,6 +693,28 @@ static int run_upload(ty_task *task)
             return r;
     }
 
+    if (ty_board_has_capability(board, TY_BOARD_CAPABILITY_RTC) && !(flags & TY_UPLOAD_NORTC)) {
+#ifdef _WIN32
+        __time64_t now;
+        struct tm ti;
+
+        _time64(&now);
+        _localtime64_s(&ti, &now);
+        now += ti.tm_gmtoff;
+#else
+        time_t now;
+        struct tm ti;
+
+        now = time(NULL);
+        localtime_r(&now, &ti);
+        now += ti.tm_gmtoff;
+#endif
+
+        r = ty_board_set_rtc(board, (int64_t)now);
+        if (r < 0)
+            return r;
+    }
+
     if (!(flags & TY_UPLOAD_NORESET)) {
         if (flags & TY_UPLOAD_DELEGATE) {
             ty_log(TY_LOG_INFO, "Waiting for Teensy Loader");
diff --git a/src/libty/board.h b/src/libty/board.h
index 153eacec..a65f3d1a 100644
--- a/src/libty/board.h
+++ b/src/libty/board.h
@@ -33,6 +33,7 @@ typedef enum ty_board_capability {
     TY_BOARD_CAPABILITY_UPLOAD,
     TY_BOARD_CAPABILITY_RESET,
     TY_BOARD_CAPABILITY_REBOOT,
+    TY_BOARD_CAPABILITY_RTC,
     TY_BOARD_CAPABILITY_SERIAL,
 
     TY_BOARD_CAPABILITY_COUNT
@@ -48,7 +49,8 @@ enum {
     TY_UPLOAD_WAIT = 1,
     TY_UPLOAD_NORESET = 2,
     TY_UPLOAD_NOCHECK = 4,
-    TY_UPLOAD_DELEGATE = 8
+    TY_UPLOAD_NORTC = 8,
+    TY_UPLOAD_DELEGATE = 16
 };
 
 #define TY_UPLOAD_MAX_FIRMWARES 256
@@ -97,6 +99,7 @@ ssize_t ty_board_serial_write(ty_board *board, const char *buf, size_t size);
 int ty_board_upload(ty_board *board, struct ty_firmware *fw, ty_board_upload_progress_func *pf, void *udata);
 int ty_board_reset(ty_board *board);
 int ty_board_reboot(ty_board *board);
+int ty_board_set_rtc(ty_board *board, int64_t time);
 
 ty_board_interface *ty_board_interface_ref(ty_board_interface *iface);
 void ty_board_interface_unref(ty_board_interface *iface);
diff --git a/src/libty/class_priv.h b/src/libty/class_priv.h
index 65d7ad9f..496e7548 100644
--- a/src/libty/class_priv.h
+++ b/src/libty/class_priv.h
@@ -32,6 +32,7 @@ struct _ty_class_vtable {
                   ty_board_upload_progress_func *pf, void *udata);
     int (*reset)(ty_board_interface *iface);
     int (*reboot)(ty_board_interface *iface);
+    int (*set_rtc)(ty_board_interface *iface, int64_t time);
 };
 
 struct _ty_class {
diff --git a/src/libty/class_teensy.c b/src/libty/class_teensy.c
index ffe24e2e..15d3e6a2 100644
--- a/src/libty/class_teensy.c
+++ b/src/libty/class_teensy.c
@@ -131,6 +131,8 @@ static int teensy_load_interface(ty_board_interface *iface)
                         iface->capabilities |= 1 << TY_BOARD_CAPABILITY_UPLOAD;
                         iface->capabilities |= 1 << TY_BOARD_CAPABILITY_RESET;
                     }
+                    if (iface->model == TY_MODEL_TEENSY_40 || iface->model == TY_MODEL_TEENSY_41)
+                        iface->capabilities |= 1 << TY_BOARD_CAPABILITY_RTC;
                 } break;
 
                 case TEENSY_USAGE_PAGE_RAWHID: {
@@ -787,6 +789,37 @@ static int teensy_reboot(ty_board_interface *iface)
     return r;
 }
 
+static int teensy_set_rtc(ty_board_interface *iface, int64_t time)
+{
+    unsigned int halfkay_version;
+    size_t min_address, max_address, block_size;
+
+    int r = get_halfkay_settings(iface->model, &halfkay_version, &min_address, &max_address, &block_size);
+    if (r < 0)
+        return r;
+
+    uint8_t buf[12];
+    {
+        unsigned long hi = (unsigned long)(time >> 17);
+        unsigned long lo = (unsigned long)(time << 15);
+
+        buf[0] = 0xB7;
+        buf[1] = 0x31;
+        buf[2] = 0xC2;
+        buf[3] = 0x89;
+        buf[4] = lo & 0xFF;
+        buf[5] = (lo >> 8) & 0xFF;
+        buf[6] = (lo >> 16) & 0xFF;
+        buf[7] = (lo >> 24) & 0xFF;
+        buf[8] = hi & 0xFF;
+        buf[9] = (hi >> 8) & 0xFF;
+        buf[10] = (hi >> 16) & 0xFF;
+        buf[11] = (hi >> 24) & 0xFF;
+    }
+
+    return halfkay_send(iface->port, halfkay_version, block_size, 0xFFFFFF, buf, sizeof(buf), 25);
+}
+
 const struct _ty_class_vtable _ty_teensy_class_vtable = {
     .load_interface = teensy_load_interface,
     .update_board = teensy_update_board,
@@ -798,5 +831,6 @@ const struct _ty_class_vtable _ty_teensy_class_vtable = {
     .serial_write = teensy_serial_write,
     .upload = teensy_upload,
     .reset = teensy_reset,
-    .reboot = teensy_reboot
+    .reboot = teensy_reboot,
+    .set_rtc = teensy_set_rtc
 };