diff --git a/flash/FLASH.md b/flash/FLASH.md
index 3fec2e3..36e70fd 100644
--- a/flash/FLASH.md
+++ b/flash/FLASH.md
@@ -155,6 +155,12 @@ Arguments. In most cases only the first two mandatory args are required:
  5. `sec_size=4096` Chip sector size.
  6. `block_size=9` The block size reported to the filesystem. The size in bytes
  is `2**block_size` so is 512 bytes by default.
+ 7. `cmdset=None` Flash chips can support two low level command sets, an old 4
+ byte set and a newer 5 byte set capable of supporting a larger address
+ space. By default if the size read from the chip's ID is <= 4096KiB the 4 byte
+ set is used oterwise the 5 byte set is adopted. This works for supported
+ chips. Setting `cmdset` `True` forces 5 byte commands, `False` forces 4 byte.
+ This override is necessary for certain chip types (e.g. WinBond W25Q64FV).
 
 Size values (KiB):  
 | Chip              | Size  |
diff --git a/flash/flash_spi.py b/flash/flash_spi.py
index c5093ec..8e61b28 100644
--- a/flash/flash_spi.py
+++ b/flash/flash_spi.py
@@ -25,7 +25,8 @@ _SEC_SIZE = const(4096)  # Flash sector size 0x1000
 # Logical Flash device comprising one or more physical chips sharing an SPI bus.
 class FLASH(FlashDevice):
 
-    def __init__(self, spi, cspins, size=None, verbose=True, sec_size=_SEC_SIZE, block_size=9):
+    def __init__(self, spi, cspins, size=None, verbose=True,
+                 sec_size=_SEC_SIZE, block_size=9, cmdset=None):
         self._spi = spi
         self._cspins = cspins
         self._ccs = None  # Chip select Pin object for current chip
@@ -42,7 +43,7 @@ class FLASH(FlashDevice):
         super().__init__(block_size, len(cspins), size * 1024, sec_size)
 
         # Select the correct command set
-        if size <= 4096:
+        if (cmdset is None and size <= 4096) or (cmdset == False):
             self._cmds = _CMDS3BA
             self._cmdlen = 4
         else: