diff --git a/tinygrad/runtime/ops_disk.py b/tinygrad/runtime/ops_disk.py
index d71bbe3609..1f810ec98f 100644
--- a/tinygrad/runtime/ops_disk.py
+++ b/tinygrad/runtime/ops_disk.py
@@ -1,4 +1,4 @@
-import os, sys, mmap, io, ctypes, ctypes.util, contextlib
+import os, sys, mmap, io, ctypes, contextlib, pathlib
 from typing import Generator, Callable
 from tinygrad.helpers import OSX, round_up
 from tinygrad.device import Compiled, Allocator
@@ -31,7 +31,7 @@ class DiskDevice(Compiled):
     else:
       try: self.fd = os.open(filename, os.O_RDWR|os.O_CREAT|getattr(os, "O_DIRECT", 0))
       except OSError: self.fd = os.open(filename, os.O_RDWR|os.O_CREAT)
-      if os.fstat(self.fd).st_size < self.size: os.ftruncate(self.fd, self.size)
+      if not pathlib.Path(filename).is_block_device() and os.fstat(self.fd).st_size < self.size: os.ftruncate(self.fd, self.size)
       self.mem = mmap.mmap(self.fd, self.size)
     if hasattr(self.mem, 'madvise') and (hp := getattr(mmap, "MADV_HUGEPAGE", None)) is not None:
       with contextlib.suppress(OSError): self.mem.madvise(hp) # some systems have transparent_hugepage disabled