diff --git a/targets/stm32l432/src/device.c b/targets/stm32l432/src/device.c
index d65b7f8..da82d8b 100644
--- a/targets/stm32l432/src/device.c
+++ b/targets/stm32l432/src/device.c
@@ -596,7 +596,7 @@ void ctap_overwrite_rk(int index,CTAP_residentKey * rk)
 
         memmove(tmppage + (sizeof(CTAP_residentKey) * index) % PAGE_SIZE, rk, sizeof(CTAP_residentKey));
         flash_erase_page(page);
-        flash_write(flash_addr(page), tmppage, ((sizeof(CTAP_residentKey) * (index + 1)) % PAGE_SIZE) );
+        flash_write(flash_addr(page), tmppage, PAGE_SIZE);
     }
     else
     {