diff --git a/test/unit/test_autogen.py b/test/unit/test_autogen.py
index 1ece479dff..086fd6adc4 100644
--- a/test/unit/test_autogen.py
+++ b/test/unit/test_autogen.py
@@ -44,4 +44,42 @@ class TestAutogen(unittest.TestCase):
       test.argtypes = [Baz]
       self.assertEqual(test(b), b.a + b.b + b.c + b.d)
 
+  @unittest.skipIf(WIN, "doesn't compile on windows")
+  def test_packed_structs(self):
+    NvU32 = ctypes.c_uint32
+    NvU64 = ctypes.c_uint64
+    class FWSECLIC_READ_VBIOS_DESC(Struct): pass
+    FWSECLIC_READ_VBIOS_DESC._packed_ = True
+    FWSECLIC_READ_VBIOS_DESC._fields_ = [
+      ('version', NvU32),
+      ('size', NvU32),
+      ('gfwImageOffset', NvU64),
+      ('gfwImageSize', NvU32),
+      ('flags', NvU32),
+    ]
+    class FWSECLIC_FRTS_REGION_DESC(Struct): pass
+    FWSECLIC_FRTS_REGION_DESC._packed_ = True
+    FWSECLIC_FRTS_REGION_DESC._fields_ = [
+      ('version', NvU32),
+      ('size', NvU32),
+      ('frtsRegionOffset4K', NvU32),
+      ('frtsRegionSize', NvU32),
+      ('frtsRegionMediaType', NvU32),
+    ]
+    class FWSECLIC_FRTS_CMD(Struct): pass
+    FWSECLIC_FRTS_CMD._packed_ = True
+    FWSECLIC_FRTS_CMD._fields_ = [
+      ('readVbiosDesc', FWSECLIC_READ_VBIOS_DESC),
+      ('frtsRegionDesc', FWSECLIC_FRTS_REGION_DESC),
+    ]
+    read_vbios_desc = FWSECLIC_READ_VBIOS_DESC(version=0x1, size=ctypes.sizeof(FWSECLIC_READ_VBIOS_DESC), flags=2)
+    frst_reg_desc = FWSECLIC_FRTS_REGION_DESC(version=0x1, size=ctypes.sizeof(FWSECLIC_FRTS_REGION_DESC),
+      frtsRegionOffset4K=0xdead, frtsRegionSize=0x100, frtsRegionMediaType=2)
+    frts_cmd = FWSECLIC_FRTS_CMD(readVbiosDesc=read_vbios_desc, frtsRegionDesc=frst_reg_desc)
+    assert int.from_bytes(frts_cmd, 'little') == 0x2000001000000dead0000001400000001000000020000000000000000000000000000001800000001
+    assert int.from_bytes(frts_cmd.readVbiosDesc, 'little') == int.from_bytes(read_vbios_desc, 'little')
+    assert int.from_bytes(frts_cmd.frtsRegionDesc, 'little') == int.from_bytes(frst_reg_desc, 'little')
+    assert frts_cmd.readVbiosDesc.__class__ is FWSECLIC_READ_VBIOS_DESC
+    assert frts_cmd.frtsRegionDesc.__class__ is FWSECLIC_FRTS_REGION_DESC
+
 if __name__ == "__main__": unittest.main()
diff --git a/tinygrad/runtime/support/c.py b/tinygrad/runtime/support/c.py
index 7e4f199fad..9f11f44042 100644
--- a/tinygrad/runtime/support/c.py
+++ b/tinygrad/runtime/support/c.py
@@ -59,7 +59,9 @@ else:
         mask = (1 << (sz:=ctypes.sizeof(ty)*8 if bf == 0 else bf)) - 1
         def fget(self, mask, off, ty): return ((int.from_bytes(self._data, sys.byteorder)>>off)&mask if issubclass(ty, _SimpleCData) else
                                                ty.from_buffer(memoryview(self._data)[(st:=off//8):st+ctypes.sizeof(ty)]))
-        def fset(self, val, mask, off): self._data[:] = (((int.from_bytes(self._data, sys.byteorder) & ~(mask<<off))|((val&mask)<<off))
+        def fset(self, val, mask, off):
+          if val.__class__ is not int: val = int.from_bytes(val, sys.byteorder)
+          self._data[:] = (((int.from_bytes(self._data, sys.byteorder) & ~(mask<<off))|((val&mask)<<off))
                                                               .to_bytes(len(self._data), sys.byteorder))
         setattr(cls, nm, property(functools.partial(fget, mask=mask, off=offset, ty=ty), functools.partial(fset, mask=mask, off=offset)))
         offset += sz