diff --git a/arch/arm/src/stm32h7/stm32_sdmmc.c b/arch/arm/src/stm32h7/stm32_sdmmc.c
index 9b7462791c8..f60a5d79121 100644
--- a/arch/arm/src/stm32h7/stm32_sdmmc.c
+++ b/arch/arm/src/stm32h7/stm32_sdmmc.c
@@ -493,7 +493,7 @@ 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);
 #endif
 static int  stm32_cancel(FAR struct sdio_dev_s *dev);