1 files changed, 1 insertions, 2 deletions
diff --git a/supervisor/shared/background_callback.c b/supervisor/shared/background_callback.c
index 288c9a4df..68a0a9667 100644
--- a/supervisor/shared/background_callback.c
+++ b/supervisor/shared/background_callback.c
@@ -33,7 +33,7 @@
 #include "supervisor/shared/tick.h"
 #include "shared-bindings/microcontroller/__init__.h"
 
-STATIC volatile background_callback_t *callback_head, *callback_tail;
+STATIC volatile background_callback_t * volatile callback_head, * volatile callback_tail;
 
 #define CALLBACK_CRITICAL_BEGIN (common_hal_mcu_disable_interrupts())
 #define CALLBACK_CRITICAL_END (common_hal_mcu_enable_interrupts())
@@ -50,7 +50,6 @@ void background_callback_add_core(background_callback_t *cb) {
     cb->prev = (background_callback_t*)callback_tail;
     if (callback_tail) {
         callback_tail->next = cb;
-        cb->prev = (background_callback_t*)callback_tail;
     }
     if (!callback_head) {
         callback_head = cb;