diff --git a/stmhal/sdcard.c b/stmhal/sdcard.c
index 22882ddb60..8952161b69 100644
--- a/stmhal/sdcard.c
+++ b/stmhal/sdcard.c
@@ -29,6 +29,7 @@
 #include <stm32f4xx_hal.h>
 
 #include "mpconfig.h"
+#include "nlr.h"
 #include "misc.h"
 #include "qstr.h"
 #include "obj.h"
@@ -36,6 +37,7 @@
 #include "sdcard.h"
 #include "pin.h"
 #include "genhdr/pins.h"
+#include "bufhelper.h"
 
 #if MICROPY_HW_HAS_SDCARD
 
@@ -154,7 +156,7 @@ bool sdcard_read_blocks(uint8_t *dest, uint32_t block_num, uint32_t num_blocks)
     // buffer and we can't let it fill up in the middle of a read.
     // This will not be needed when SD uses DMA for transfer.
     __disable_irq();
-    HAL_SD_ErrorTypedef err = HAL_SD_ReadBlocks(&sd_handle, (uint32_t*)dest, block_num * SDCARD_BLOCK_SIZE, SDCARD_BLOCK_SIZE, num_blocks);
+    HAL_SD_ErrorTypedef err = HAL_SD_ReadBlocks(&sd_handle, (uint32_t*)dest, (uint64_t)block_num * SDCARD_BLOCK_SIZE, SDCARD_BLOCK_SIZE, num_blocks);
     __enable_irq();
 
     if (err != SD_OK) {
@@ -179,7 +181,7 @@ bool sdcard_write_blocks(const uint8_t *src, uint32_t block_num, uint32_t num_bl
     // buffer and we can't let it drain to empty in the middle of a write.
     // This will not be needed when SD uses DMA for transfer.
     __disable_irq();
-    HAL_SD_ErrorTypedef err = HAL_SD_WriteBlocks(&sd_handle, (uint32_t*)src, block_num * SDCARD_BLOCK_SIZE, SDCARD_BLOCK_SIZE, num_blocks);
+    HAL_SD_ErrorTypedef err = HAL_SD_WriteBlocks(&sd_handle, (uint32_t*)src, (uint64_t)block_num * SDCARD_BLOCK_SIZE, SDCARD_BLOCK_SIZE, num_blocks);
     __enable_irq();
 
     if (err != SD_OK) {
@@ -203,7 +205,7 @@ bool sdcard_read_blocks_dma(uint8_t *dest, uint32_t block_num, uint32_t num_bloc
     }
 
     // do the read
-    if (HAL_SD_ReadBlocks_DMA(&sd_handle, (uint32_t*)dest, block_num * SDCARD_BLOCK_SIZE, SDCARD_BLOCK_SIZE) != SD_OK) {
+    if (HAL_SD_ReadBlocks_DMA(&sd_handle, (uint32_t*)dest, (uint64_t)block_num * SDCARD_BLOCK_SIZE, SDCARD_BLOCK_SIZE) != SD_OK) {
         return false;
     }
 
@@ -228,7 +230,7 @@ bool sdcard_write_blocks_dma(const uint8_t *src, uint32_t block_num, uint32_t nu
 
     SD_Error status;
 
-    status = HAL_SD_WriteBlock_DMA(&sd_handle, (uint32_t*)src, block_num * SDCARD_BLOCK_SIZE, SDCARD_BLOCK_SIZE, num_blocks);
+    status = HAL_SD_WriteBlock_DMA(&sd_handle, (uint32_t*)src, (uint64_t)block_num * SDCARD_BLOCK_SIZE, SDCARD_BLOCK_SIZE, num_blocks);
     if (status != SD_OK) {
         return false;
     }
@@ -276,10 +278,28 @@ static mp_obj_t sd_read(mp_obj_t self, mp_obj_t block_num) {
 
 static MP_DEFINE_CONST_FUN_OBJ_2(sd_read_obj, sd_read);
 
+static mp_obj_t sd_write(mp_obj_t self, mp_obj_t block_num, mp_obj_t source) {
+    mp_buffer_info_t bufinfo;
+    uint8_t tmp[1];
+
+    pyb_buf_get_for_send(source, &bufinfo, tmp);
+    if (bufinfo.len % SDCARD_BLOCK_SIZE != 0) {
+        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "writes must be aligned to SDCARD_BLOCK_SIZE (%d) bytes", SDCARD_BLOCK_SIZE));
+    }
+
+    if (!sdcard_write_blocks(bufinfo.buf, mp_obj_get_int(block_num), bufinfo.len / SDCARD_BLOCK_SIZE)) {
+        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_Exception, "sdcard_write_blocks failed"));
+    }
+    return mp_const_none;
+}
+
+static MP_DEFINE_CONST_FUN_OBJ_3(sd_write_obj, sd_write);
+
 STATIC const mp_map_elem_t sdcard_locals_dict_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR_present), (mp_obj_t)&sd_present_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_power), (mp_obj_t)&sd_power_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_read), (mp_obj_t)&sd_read_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_write), (mp_obj_t)&sd_write_obj },
 };
 
 STATIC MP_DEFINE_CONST_DICT(sdcard_locals_dict, sdcard_locals_dict_table);