diff --git a/fatfs/shimatta_sdio_driver/shimatta_sdio.c b/fatfs/shimatta_sdio_driver/shimatta_sdio.c
index 7386221..ebf48a5 100644
--- a/fatfs/shimatta_sdio_driver/shimatta_sdio.c
+++ b/fatfs/shimatta_sdio_driver/shimatta_sdio.c
@@ -181,10 +181,10 @@ static int sdio_send_csd_cmd9(uint16_t rca, uint32_t *response_buffer) {
 /**
  * @brief Send data buffer to SD card
  * @param dlen Data length. Must be a multiple of 4 bytes
- * @param blklen Block length
+ * @param blklen Log2 of block length (9 in case of 512 byte block)
  * @param buff Buffer to send
  */
-static void sdio_write_buffer(uint32_t dlen, uint32_t blklen, uint8_t *buff)
+static void sdio_write_buffer(uint32_t dlen, uint32_t log_blklen, const unsigned char *buff)
 {
 	uint32_t count;
 	int byte_count;
@@ -197,7 +197,7 @@ static void sdio_write_buffer(uint32_t dlen, uint32_t blklen, uint8_t *buff)
 	SDIO->ICR = SDIO_ICR_CCRCFAILC | SDIO_ICR_DCRCFAILC | SDIO_ICR_CTIMEOUTC | SDIO_ICR_DTIMEOUTC |
 			SDIO_ICR_TXUNDERRC | SDIO_ICR_RXOVERRC | SDIO_ICR_CMDRENDC | SDIO_ICR_CMDSENTC | SDIO_ICR_DATAENDC |
 			SDIO_ICR_STBITERRC | SDIO_ICR_DBCKENDC | SDIO_ICR_SDIOITC | SDIO_ICR_CEATAENDC;
-	SDIO->DCTRL = (blklen<<4) | SDIO_DCTRL_DTEN;
+	SDIO->DCTRL = (log_blklen<<4) | SDIO_DCTRL_DTEN;
 
 	for (count = 0; count < dlen; count += 4) {
 		fifo = 0;
@@ -225,9 +225,11 @@ static void sdio_write_buffer(uint32_t dlen, uint32_t blklen, uint8_t *buff)
 
 static int sdio_send_write_block_cmd24(uint32_t addr)
 {
-	(void)addr;
+	uint32_t response;
 
-	return -1;
+	sdio_send_cmd(24, addr, SHORT_ANS);
+
+	return sdio_get_response(24, SHORT_ANS, &response);
 }
 
 static int sdio_check_status_register_cmd13(uint16_t rca, uint32_t *status)
@@ -691,5 +693,41 @@ DRESULT sdio_disk_read(BYTE *buff, DWORD sector, UINT count){
  */
 DRESULT sdio_disk_write(const BYTE *buff, DWORD sector, UINT count)
 {
-	return RES_ERROR;
+	uint32_t addr;
+	union sdio_status_conv status;
+	uint32_t buff_offset = 0;
+	int ret;
+
+	if (sdio_check_write_protection())
+		return RES_WRPRT;
+
+	addr = (card_info.type == SD_V2_HC ? (sector) : (sector * 512));
+
+	while (count) {
+		do {
+			sdio_check_status_register_cmd13(card_info.rca, &status.value);
+		} while (status.statusstruct.CURRENT_STATE == CURRENT_STATE_PRG ||
+			 status.statusstruct.CURRENT_STATE == CURRENT_STATE_RCV);
+
+		if (status.statusstruct.CURRENT_STATE == CURRENT_STATE_STBY) {
+			if (sdio_send_select_card_cmd7(card_info.rca))
+				return RES_ERROR;
+		}
+
+		do {
+			sdio_check_status_register_cmd13(card_info.rca, &status.value);
+		} while (status.statusstruct.READY_FOR_DATA != 1);
+
+		ret = sdio_send_write_block_cmd24(addr);
+		if (ret) {
+			return RES_ERROR;
+		}
+		sdio_write_buffer(512, 9, &buff[buff_offset]);
+
+		buff_offset += 512;
+		addr += (card_info.type == SD_V2_HC ? 1 : 512);
+		count--;
+	}
+
+	return RES_OK;
 }
diff --git a/include/fatfs/ffconf.h b/include/fatfs/ffconf.h
index 3145b9b..926378a 100644
--- a/include/fatfs/ffconf.h
+++ b/include/fatfs/ffconf.h
@@ -8,7 +8,7 @@
 / Function Configurations
 /---------------------------------------------------------------------------*/
 
-#define FF_FS_READONLY	1
+#define FF_FS_READONLY	0
 /* This option switches read-only configuration. (0:Read/Write or 1:Read-only)
 /  Read-only configuration removes writing API functions, f_write(), f_sync(),
 /  f_unlink(), f_mkdir(), f_chmod(), f_rename(), f_truncate(), f_getfree()
diff --git a/main.c b/main.c
index afc193a..95eb545 100644
--- a/main.c
+++ b/main.c
@@ -26,6 +26,8 @@ int main() {
 	char buff[1024];
 	char *name;
 	FILINFO fno;
+	char *write_string = "This is a write test. Okay... Writing seems to work. Let's close the file\n";
+
 	RCC->AHB1ENR |= RCC_AHB1ENR_GPIOAEN;
 	__DSB();
 	GPIOA->MODER |= OUTPUT(6) | OUTPUT(7);
@@ -53,6 +55,13 @@ int main() {
 
 		}
 	}
+
+	initreq = f_open(&file, "foo.txt", FA_OPEN_APPEND | FA_WRITE);
+	if (initreq == FR_OK) {
+		initreq = f_write(&file, write_string, strlen(write_string), NULL);
+		initreq = f_close(&file);
+	}
+
 //fflush(stdout);
 
 while(1);