diff --git a/SDBlockDevice.cpp b/SDBlockDevice.cpp
index 2cf40984c0..ba45dc296c 100644
--- a/SDBlockDevice.cpp
+++ b/SDBlockDevice.cpp
@@ -232,7 +232,7 @@
 #define SPI_READ_ERROR_ECC_C     (0x1 << 2)  /*!< Card ECC failed */
 #define SPI_READ_ERROR_OFR       (0x1 << 3)  /*!< Out of Range */
 
-SDBlockDevice::SDBlockDevice(PinName mosi, PinName miso, PinName sclk, PinName cs)
+SDBlockDevice::SDBlockDevice(PinName mosi, PinName miso, PinName sclk, PinName cs, uint64_t hz)
     : _spi(mosi, miso, sclk), _cs(cs), _is_initialized(0)
 {
     _cs = 1;
@@ -240,7 +240,7 @@ SDBlockDevice::SDBlockDevice(PinName mosi, PinName miso, PinName sclk, PinName c
 
     // Set default to 100kHz for initialisation and 1MHz for data transfer
     _init_sck = 100000;
-    _transfer_sck = 1000000;
+    _transfer_sck = hz;
 
     // Only HC block size is supported.
     _block_size = BLOCK_SIZE_HC;
diff --git a/SDBlockDevice.h b/SDBlockDevice.h
index 17775720d4..8d46a986de 100644
--- a/SDBlockDevice.h
+++ b/SDBlockDevice.h
@@ -50,7 +50,7 @@ class SDBlockDevice : public BlockDevice {
 public:
     /** Lifetime of an SD card
      */
-    SDBlockDevice(PinName mosi, PinName miso, PinName sclk, PinName cs);
+    SDBlockDevice(PinName mosi, PinName miso, PinName sclk, PinName cs, uint64_t hz=1000000);
     virtual ~SDBlockDevice();
 
     /** Initialize a block device