diff --git a/libraries/USBHost/USBHostMSD/USBHostMSD.cpp b/libraries/USBHost/USBHostMSD/USBHostMSD.cpp
index 75d0f59d4b..1fcb54abf8 100644
--- a/libraries/USBHost/USBHostMSD/USBHostMSD.cpp
+++ b/libraries/USBHost/USBHostMSD/USBHostMSD.cpp
@@ -323,14 +323,14 @@ int USBHostMSD::disk_initialize() {
     return readCapacity();
 }
 
-int USBHostMSD::disk_write(const uint8_t* buffer, uint32_t block_number, uint32_t count) {
+int USBHostMSD::disk_write(const uint8_t* buffer, uint64_t block_number, uint8_t count) {
     USB_DBG("FILESYSTEM: write block: %lld, count: %d", block_number, count);
     if (!disk_init) {
         disk_initialize();
     }
     if (!disk_init)
         return -1;
-    for (uint32_t b = block_number; b < block_number + count; b++) {
+    for (uint64_t b = block_number; b < block_number + count; b++) {
         if (dataTransfer((uint8_t*)buffer, b, 1, HOST_TO_DEVICE))
             return -1;
         buffer += 512;
@@ -338,14 +338,14 @@ int USBHostMSD::disk_write(const uint8_t* buffer, uint32_t block_number, uint32_
     return 0;
 }
 
-int USBHostMSD::disk_read(uint8_t* buffer, uint32_t block_number, uint32_t count) {
+int USBHostMSD::disk_read(uint8_t* buffer, uint64_t block_number, uint8_t count) {
     USB_DBG("FILESYSTEM: read block: %lld, count: %d", block_number, count);
     if (!disk_init) {
         disk_initialize();
     }
     if (!disk_init)
         return -1;
-    for (uint32_t b = block_number; b < block_number + count; b++) {
+    for (uint64_t b = block_number; b < block_number + count; b++) {
         if (dataTransfer((uint8_t*)buffer, b, 1, DEVICE_TO_HOST))
             return -1;
         buffer += 512;
@@ -353,7 +353,7 @@ int USBHostMSD::disk_read(uint8_t* buffer, uint32_t block_number, uint32_t count
     return 0;
 }
 
-uint32_t USBHostMSD::disk_sectors() {
+uint64_t USBHostMSD::disk_sectors() {
     USB_DBG("FILESYSTEM: sectors");
     if (!disk_init) {
         disk_initialize();
diff --git a/libraries/USBHost/USBHostMSD/USBHostMSD.h b/libraries/USBHost/USBHostMSD/USBHostMSD.h
index 667ad17191..10c6025857 100644
--- a/libraries/USBHost/USBHostMSD/USBHostMSD.h
+++ b/libraries/USBHost/USBHostMSD/USBHostMSD.h
@@ -59,10 +59,10 @@ protected:
     // From FATFileSystem
     virtual int disk_initialize();
     virtual int disk_status() {return 0;};
-    virtual int disk_read(uint8_t* buffer, uint32_t sector, uint32_t count);
-    virtual int disk_write(const uint8_t* buffer, uint32_t sector, uint32_t count);
+    virtual int disk_read(uint8_t* buffer, uint64_t sector, uint8_t count);
+    virtual int disk_write(const uint8_t* buffer, uint64_t sector, uint8_t count);
     virtual int disk_sync() {return 0;};
-    virtual uint32_t disk_sectors();
+    virtual uint64_t disk_sectors();
 
 private:
     USBHost * host;
@@ -104,7 +104,7 @@ private:
     int getMaxLun();
 
     int blockSize;
-    uint32_t blockCount;
+    uint64_t blockCount;
 
     int msd_intf;
     bool msd_device_found;
diff --git a/libraries/fs/fat/ChaN/diskio.cpp b/libraries/fs/fat/ChaN/diskio.cpp
index 50c4a72fe7..6b3284cd39 100644
--- a/libraries/fs/fat/ChaN/diskio.cpp
+++ b/libraries/fs/fat/ChaN/diskio.cpp
@@ -36,7 +36,7 @@ DRESULT disk_read (
 )
 {
     debug_if(FFS_DBG, "disk_read(sector %d, count %d) on pdrv [%d]\n", sector, count, pdrv);
-    if (FATFileSystem::_ffs[pdrv]->disk_read(buff, sector, count))
+    if (FATFileSystem::_ffs[pdrv]->disk_read((uint8_t*)buff, sector, count))
         return RES_PARERR;
     else
         return RES_OK;
@@ -51,7 +51,7 @@ DRESULT disk_write (
 )
 {
     debug_if(FFS_DBG, "disk_write(sector %d, count %d) on pdrv [%d]\n", sector, count, pdrv);
-    if (FATFileSystem::_ffs[pdrv]->disk_write(buff, sector, count))
+    if (FATFileSystem::_ffs[pdrv]->disk_write((uint8_t*)buff, sector, count))
         return RES_PARERR;
     else
         return RES_OK;
diff --git a/libraries/fs/fat/FATFileSystem.h b/libraries/fs/fat/FATFileSystem.h
index 51009651ad..0c6708e44b 100644
--- a/libraries/fs/fat/FATFileSystem.h
+++ b/libraries/fs/fat/FATFileSystem.h
@@ -84,10 +84,10 @@ public:
 
     virtual int disk_initialize() { return 0; }
     virtual int disk_status() { return 0; }
-    virtual int disk_read(uint8_t * buffer, uint32_t sector, uint32_t count) = 0;
-    virtual int disk_write(const uint8_t * buffer, uint32_t sector, uint32_t count) = 0;
+    virtual int disk_read(uint8_t * buffer, uint64_t sector, uint8_t count) = 0;
+    virtual int disk_write(const uint8_t * buffer, uint64_t sector, uint8_t count) = 0;
     virtual int disk_sync() { return 0; }
-    virtual uint32_t disk_sectors() = 0;
+    virtual uint64_t disk_sectors() = 0;
 
 };
 
diff --git a/libraries/fs/sd/SDFileSystem.cpp b/libraries/fs/sd/SDFileSystem.cpp
index 27a698d42a..054035553d 100644
--- a/libraries/fs/sd/SDFileSystem.cpp
+++ b/libraries/fs/sd/SDFileSystem.cpp
@@ -223,12 +223,12 @@ int SDFileSystem::disk_initialize() {
     return 0;
 }
 
-int SDFileSystem::disk_write(const uint8_t* buffer, uint32_t block_number, uint32_t count) {
+int SDFileSystem::disk_write(const uint8_t* buffer, uint64_t block_number, uint8_t count) {
     if (!_is_initialized) {
         return -1;
     }
     
-    for (uint32_t b = block_number; b < block_number + count; b++) {
+    for (uint64_t b = block_number; b < block_number + count; b++) {
         // set write address for single block (CMD24)
         if (_cmd(24, b * cdv) != 0) {
             return 1;
@@ -242,12 +242,12 @@ int SDFileSystem::disk_write(const uint8_t* buffer, uint32_t block_number, uint3
     return 0;
 }
 
-int SDFileSystem::disk_read(uint8_t* buffer, uint32_t block_number, uint32_t count) {
+int SDFileSystem::disk_read(uint8_t* buffer, uint64_t block_number, uint8_t count) {
     if (!_is_initialized) {
         return -1;
     }
     
-    for (uint32_t b = block_number; b < block_number + count; b++) {
+    for (uint64_t b = block_number; b < block_number + count; b++) {
         // set read address for single block (CMD17)
         if (_cmd(17, b * cdv) != 0) {
             return 1;
@@ -271,7 +271,7 @@ int SDFileSystem::disk_status() {
 }
 
 int SDFileSystem::disk_sync() { return 0; }
-uint32_t SDFileSystem::disk_sectors() { return _sectors; }
+uint64_t SDFileSystem::disk_sectors() { return _sectors; }
 
 
 // PRIVATE FUNCTIONS
@@ -443,11 +443,11 @@ static uint32_t ext_bits(unsigned char *data, int msb, int lsb) {
     return bits;
 }
 
-uint32_t SDFileSystem::_sd_sectors() {
+uint64_t SDFileSystem::_sd_sectors() {
     uint32_t c_size, c_size_mult, read_bl_len;
     uint32_t block_len, mult, blocknr, capacity;
     uint32_t hc_c_size;
-    uint32_t blocks;
+    uint64_t blocks;
 
     // CMD9, Response R2 (R1 byte + 16-byte block read)
     if (_cmdx(9, 0) != 0) {
diff --git a/libraries/fs/sd/SDFileSystem.h b/libraries/fs/sd/SDFileSystem.h
index 24e6cdaf03..73aba494d7 100644
--- a/libraries/fs/sd/SDFileSystem.h
+++ b/libraries/fs/sd/SDFileSystem.h
@@ -54,10 +54,10 @@ public:
     SDFileSystem(PinName mosi, PinName miso, PinName sclk, PinName cs, const char* name);
     virtual int disk_initialize();
     virtual int disk_status();
-    virtual int disk_read(uint8_t* buffer, uint32_t block_number, uint32_t count);
-    virtual int disk_write(const uint8_t* buffer, uint32_t block_number, uint32_t count);
+    virtual int disk_read(uint8_t* buffer, uint64_t block_number, uint8_t count);
+    virtual int disk_write(const uint8_t* buffer, uint64_t block_number, uint8_t count);
     virtual int disk_sync();
-    virtual uint32_t disk_sectors();
+    virtual uint64_t disk_sectors();
 
 protected:
 
@@ -71,8 +71,8 @@ protected:
 
     int _read(uint8_t * buffer, uint32_t length);
     int _write(const uint8_t *buffer, uint32_t length);
-    uint32_t _sd_sectors();
-    uint32_t _sectors;
+    uint64_t _sd_sectors();
+    uint64_t _sectors;
 
     void set_init_sck(uint32_t sck) { _init_sck = sck; }
     // Note: The highest SPI clock rate is 20 MHz for MMC and 25 MHz for SD