diff --git a/stmhal/main.c b/stmhal/main.c
index 9f48fbfd65..947c25b41e 100644
--- a/stmhal/main.c
+++ b/stmhal/main.c
@@ -549,6 +549,8 @@ soft_reset:
     printf("PYB: sync filesystems\n");
     storage_flush();
 
+    timer_deinit();
+
     printf("PYB: soft reboot\n");
 
     first_soft_reset = false;
diff --git a/stmhal/timer.c b/stmhal/timer.c
index ec0c4dec4c..8634c46bf2 100644
--- a/stmhal/timer.c
+++ b/stmhal/timer.c
@@ -366,13 +366,20 @@ STATIC mp_obj_t pyb_timer_init(uint n_args, const mp_obj_t *args, mp_map_t *kw_a
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_KW(pyb_timer_init_obj, 1, pyb_timer_init);
 
+STATIC mp_obj_t pyb_timer_callback(mp_obj_t self_in, mp_obj_t callback);
+
 /// \method deinit()
 /// Deinitialises the timer.
 ///
-/// *This function is not yet implemented.*
+/// Disables the callback (and the associated irq).
+/// Stops the timer, and disables the timer peripheral.
 STATIC mp_obj_t pyb_timer_deinit(mp_obj_t self_in) {
-    //pyb_timer_obj_t *self = self_in;
-    // TODO implement me
+    pyb_timer_obj_t *self = self_in;
+
+    // Disable the interrupt
+    pyb_timer_callback(self_in, mp_const_none);
+
+    HAL_TIM_Base_DeInit(&self->tim);
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(pyb_timer_deinit_obj, pyb_timer_deinit);
@@ -464,6 +471,16 @@ const mp_obj_type_t pyb_timer_type = {
     .locals_dict = (mp_obj_t)&pyb_timer_locals_dict,
 };
 
+// Unregister all interrupt sources
+void timer_deinit(void) {
+    for (uint i = 0; i < PYB_TIMER_OBJ_ALL_NUM; i++) {
+        pyb_timer_obj_t *tim = pyb_timer_obj_all[i];
+        if (tim != NULL) {
+            pyb_timer_deinit(tim);
+        }
+    }
+}
+
 void timer_irq_handler(uint tim_id) {
     if (tim_id - 1 < PYB_TIMER_OBJ_ALL_NUM) {
         // get the timer object
diff --git a/stmhal/timer.h b/stmhal/timer.h
index 9b19d1cd12..2a892db285 100644
--- a/stmhal/timer.h
+++ b/stmhal/timer.h
@@ -40,4 +40,6 @@ void timer_tim3_init(void);
 void timer_tim5_init(void);
 void timer_tim6_init(uint freq);
 
+void timer_deinit(void);
+
 void timer_irq_handler(uint tim_id);