diff --git a/shared-bindings/sdcardio/SDCard.c b/shared-bindings/sdcardio/SDCard.c
index 2802499956c36..9a04cea57e594 100644
--- a/shared-bindings/sdcardio/SDCard.c
+++ b/shared-bindings/sdcardio/SDCard.c
@@ -43,6 +43,13 @@
 //|            Failure to do so can prevent the SD card from being recognized until it is
 //|            powered off or re-inserted.
 //|
+//|            Exception: on boards where another SPI peripheral has a floating CS
+//|            pin with no hardware pull-up (such as the Feather RP2040 RFM), that
+//|            peripheral's CS must be driven HIGH before SD card initialization.
+//|            Failure to do so will corrupt the SPI bus during SD card init. In
+//|            these cases, initialize and drive the other peripheral's CS high
+//|            first, then initialize the SD card.
+//|
 //|         Example usage:
 //|
 //|         .. code-block:: python