diff --git a/stm32/mk4-bootloader/sdcard.c b/stm32/mk4-bootloader/sdcard.c
index 626fe295..64127c66 100644
--- a/stm32/mk4-bootloader/sdcard.c
+++ b/stm32/mk4-bootloader/sdcard.c
@@ -124,6 +124,7 @@ sdcard_probe(uint32_t *num_blocks)
 sdcard_is_inserted(void)
 {
 #ifdef FOR_Q1_ONLY
+    // XXX check pin; also force mux to A
     return !!HAL_GPIO_ReadPin(GPIOD, GPIO_PIN_3);       // PD3
 #else
     return !!HAL_GPIO_ReadPin(GPIOC, GPIO_PIN_13);      // PC13