diff --git a/arch/arm/src/stm32/stm32_sdio.c b/arch/arm/src/stm32/stm32_sdio.c
index b1150b61a6e..ec529b957e0 100644
--- a/arch/arm/src/stm32/stm32_sdio.c
+++ b/arch/arm/src/stm32/stm32_sdio.c
@@ -458,7 +458,7 @@ static void stm32_blocksetup(FAR struct sdio_dev_s *dev,
 static int  stm32_recvsetup(FAR struct sdio_dev_s *dev, FAR uint8_t *buffer,
               size_t nbytes);
 static int  stm32_sendsetup(FAR struct sdio_dev_s *dev,
-              FAR const uint8_t *buffer, uint32_t nbytes);
+              FAR const uint8_t *buffer, size_t nbytes);
 static int  stm32_cancel(FAR struct sdio_dev_s *dev);
 
 static int  stm32_waitresponse(FAR struct sdio_dev_s *dev, uint32_t cmd);